Platen pump

ABSTRACT

Disclosed is an infusion pump for expelling a fluid from a collapsible fluid reservoir to a patient. The pump includes a housing having a chamber therein for receiving the fluid reservoir. A first wall is provided on the housing for contacting the fluid reservoir, and a second wall is movable from a first position distanced from the first wall to form the chamber therebetween, and a second position relatively closer to the first wall. Advancing the movable wall from the first position to the second position expels fluid from the collapsible reservoir at a substantially constant rate by applying increasing force on the fluid reservoir through the dispensation cycle. Preferably, the first and second walls are provided with non-planar complementary surface configurations for contacting the collapsible reservoir. Retraction mechanisms for retracting the movable wall from the second position to the first position, and user readable indicium of the status of the dispensation cycle are also disclosed.

This application is a continuation application of U.S. patentapplication Ser. No. 08/617,679, filed Mar. 19, 1996, now abandonedwhich is a continuation-in-part of U.S. patent application Ser. No.08/385,083, filed Feb. 7, 1995, now abandoned, which is a continuationof U.S. patent application Ser. No. 08/008,790, filed Jan. 22, 1993, nowabandoned, which is a continuation-in-part of U.S. patent applicationSer. No. 07/898,958, filed Jun. 15, 1992, now abandoned, which is acontinuation-in-part of U.S. patent application Ser. No. 07/824,855,filed Jan. 24, 1992, now U.S. Pat. No. 5,911,716.

FIELD OF THE INVENTION

This invention relates to a low cost drug delivery system useful indelivering drugs, from pliable plastic containers.

BACKGROUND OF THE INVENTION

Many drugs in the healthcare field are administered to a patient on acontinuous basis. Continuous delivery of a drug to a patient wasinitially achieved by placing a drug delivery bag filled with a drugabove the patient and letting gravity force the drug from the bag intothe patient. Although this method has proven successful for manyapplications, its drawbacks included a) an unsteady flow to the patientdue to the changing height of the intravenous infusion site relative tothe drug bag, b) the awkwardness of requiring the patient to remainbelow the fluid delivery bag at all times, and c) the constantadjustment of a roller clamp which regulates the flow to the patient.Electromechanical infusion pumps were developed to mitigate theseconcerns. However, the utility of such pumps was hindered by their bulkysize and by their need for a constant source of electricity. Thesehindrances are especially troublesome in situations where a patient isat home and ambulatory, thus requiring the freedom to move about.

During the past five years, a new style of apparatus has entered themarketplace for controlled delivery of a drug which does not require theuse of an electromechanical infusion pump, and thus is suited for thecontrolled delivery of drugs to patients who are ambulatory. This newstyle utilizes an inflatable latex rubber balloon housed inside a rigid,clear plastic housing. When the devices are filled with a drug, thelatex balloon expands. An administration set is attached to the deviceand thus acts as the conduit for the drug to the patient. When theballoon is inflated by the drug, the balloon itself becomes the drivingforce to transfer the drug out of the reservoir to the patient via thedrug administration set. Controlled release of the drug at a desiredflow rate is achieved by placing an orifice of predetermined diameter inthe drug line. These devices generally operated at a relatively highpressures of approximately 10 to 15 psi. Examples of the latex balloonsystem are disclosed in U.S. Pat. Nos. 4,769,008 and 4,915,693 andEuropean Patent Application 0,426,319 A2.

Although the latex balloon method of drug delivery has certainadvantages over the electromechanical infusion pump, the method also hasits disadvantages. For example, because the balloon expands in alldirections, the shape of the housing enclosing the balloon is round.This round shape does not conform well to the patient when worn in thepatient's pocket. Furthermore, some of the latex balloon style devicesrequire a special machine to fill and pressurize the balloon with adrug. Consequently, the pharmacist must use the special machine to loadthe device. Thus, there exists the need for a safe, economical drugdelivery system which could (a) be inconspicuously and comfortably wornby the patient, (b) allow the pharmacist to fill the drug containerwithout the use of a special pressurizing device, (c) allow the nurse orpatient to load the drug container into the pressurizing device, (d)allow for reuse of parts of the system.

SUMMARY OF THE INVENTION

The present invention allows the use of standard, rectangular medicationbags to be used in a platen pump. By using the standard bags, hospitalsdo not have to maintain a large inventory of medication bags ofdiffering size and shape.

One aspect of the present invention is an infusion pump for expelling afluid from a fluid reservoir. The infusion pump comprises a housinghaving a chamber therein for receiving a fluid reservoir and a firstwall for contacting the fluid reservoir. A second wall is movablebetween a first position distanced from the first wall to form thechamber therebetween, and a second position relatively closer to thefirst wall. The second wall is moved by a parallelogram linkage. Theparallelogram linkage comprises at least one spring for biasing theparallelogram linkage. The movement of the parallelogram linkage causesthe second wall to advance toward the first wall. Importantly, theadvancement of the second wall provides increased force on the fluidreservoir through the dispensation cycle thereby achieving a constantflow rate.

In another embodiment, the present invention is an infusion pumpcomprising a housing having a chamber therein for receiving a fluidreservoir. The pump contains a first wall for contacting the fluidreservoir and a second wall movable between a first position distancedfrom the first wall to form the chamber therebetween, and a secondposition relatively closer to the first wall. The pump includes acompression means for moving the second wall, wherein the compressionmeans achieves a substantially constant flow rate from the fluidreservoir by increasing the force applied to the fluid reservoir as thesecond wall moves toward the second position.

In another embodiment, the present invention provides an infusion pumpfor expelling fluid from a flexible reservoir comprising a top shell, abottom shell, a pressure plate, a shaft, a first slide, a second slide,four arms, and a biasing means. The top shell is removably connected tothe bottom shell, the bottom shell having a non-planar interior bottomsurface. The pressure plate is movably connected to the top shell. Theplate has a non-planar surface complementary to the interior bottomsurface of the bottom shell. A variable-sized area is defined betweenthe pressure plate and the interior bottom surface of the bottom shell,the area generally capable of accepting the fluid reservoir therein. Theshaft is positioned between the top and bottom shells, and has a firstend and a second end. The first and second slides are slidablypositioned on the shaft. The four arms define a parallelogram structureextending between the top shell, the first slide, the second slide, andthe pressure plate. The arms are rotatably connected to the top shell,the slide members, and the pressure plate. The slide members and shaftare supported by the arms between the shells. The biasing means arepositioned between the first end of the shaft and the first slide, andbetween the second end of the shaft and the second slide, for biasingthe slides toward one another along the shaft, thereby biasing thepressure plate through the arms, downwardly towards the bottom shellwhen the top and bottom shells are connected.

In yet another embodiment, the present invention provides an infusionpump for expelling fluid from a fluid reservoir, comprising a housing, aplaten member, first through fourth arms, and first and second springs.The housing comprises a bottom member having a non-planar inner surfaceand a top member removably connected to the bottom member. The platenmember is movably connected to the top member. The platen has anon-planar engaging surface which is complementary in shape to the innersurface of the bottom member. The first arm has a first end and a secondend, the first end rotatably connected to the top member and the secondend rotatably connected to a first mounting block. The second arm has afirst end and a second end, the first end rotatably connected to the topmember and the second end rotatably connected to a second mountingblock. The shaft has a first end and a second end and extends throughthe blocks. The first spring extends between the first end of the shaftand the first block. The second spring extends between the second end ofthe shaft and the second block. The third arm has a first end and asecond end, the first end rotatably connected to the first block and thesecond end rotatably connected to the platen member. The fourth arm hasa first end and a second end, the first end rotatably connected to thesecond block and the second end rotatably connected to the platenmember. The arms form a linkage between the top member, the blocks, andthe platen member, biasing the platen member downwardly towards thebottom member when the top and bottom members are connected.

Further features and advantages of the present invention will becomeapparent to one of skill in the art from a review of the DetailedDescription of Preferred Embodiments which follows, when considered withthe attached claims and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of the infusion device of the presentinvention.

FIG. 2 is a partial cross-sectional view of the infusion device of FIG.1 with the shells not engaged.

FIG. 3 is a side cross-sectional view of the top shell of FIG. 2.

FIG. 4 is a cross-sectional view of the infusion device of FIG. 1 withthe shells fully engaged.

FIG. 5a and 5 b are a plan view and side view, respectively, of therotatable spring retainer used in the infusion devices of FIG. 1.

FIGS. 6a and 6 b are a plan view and side view, respectively, of theplaten used in the infusion device of FIG. 1.

FIG. 7 is a plan view of the fluid delivery bag of the presentinvention.

FIG. 8 is an isometric view of an alternate embodiment of the infusiondevice of the present invention.

FIG. 8a is a cross-sectional view of the infusion device of FIG. 8 in anopen position.

FIG. 8b is a cross-sectional view of the infusion device of FIG. 8 in aclosed position.

FIG. 9 is a top perspective view of a dual concentric platen embodimentof the infusion pump in accordance with the present invention.

FIG. 10 is an elevational cross-sectional view of the pump illustratedin FIG. 9.

FIG. 11 is an elevational cross-sectional view of the pump illustratedin FIG. 9, partway through the dispensation cycle.

FIG. 12 is an elevational cross-sectional view of the pump illustratedin FIG. 9, at the completion of the dispensation cycle.

FIG. 13 is an elevational cross-sectional view of a multi-segment platenembodiment in accordance with the present invention, at the commencementof the dispensation cycle.

FIG. 14 is a cross-sectional elevational view of the pump of FIG. 13,partway through the dispensation cycle.

FIG. 15 is a cross-sectional elevational view of the pump illustrated inFIG. 13, at the completion of the dispensation cycle.

FIG. 16 is a top plan view of a multi-segment platen in accordance withone aspect of the invention.

FIG. 17 is a top plan view of an alternate multi-segment platen.

FIG. 18 is an elevational cross-sectional view of a lever assistedspring retractor in accordance with the present invention.

FIG. 19 is an elevational cross-sectional view of the embodiment of FIG.18, with the platen in the retracted position.

FIG. 20 is an elevational cross-sectional view of the embodiment of FIG.18, at the commencement of the dispensation cycle.

FIG. 21 is an elevational cross-sectional view of a key-operated platenretractor in accordance with the present invention.

FIG. 22 is an elevational cross-sectional view of the embodiment of FIG.21, with a key in place.

FIG. 23 is an elevational cross-sectional view of the embodiment in FIG.21, at the commencement of the dispensation cycle.

FIG. 24 is an alternate embodiment of the design illustrated in FIG. 23.

FIG. 25 is an elevational cross-sectional view of an infusion pumphaving a collapsible platen retractor.

FIG. 26 is an elevational cross-sectional view of the pump of FIG. 25,at the completion of the dispensation cycle.

FIG. 27 is an elevational cross-sectional view of an ultra-low profilepump in accordance with the present invention.

FIG. 28 is an elevational cross-sectional view of the pump of FIG. 27,with the platen fully retracted.

FIG. 29 is an elevational cross-sectional view of the pump of FIG. 27,at the commencement of the dispensation cycle.

FIG. 30 is an elevational view of the pump illustrated in FIG. 29.

FIG. 31 is an elevational cross-sectional view of an alternate platenretractor in accordance with the present invention.

FIG. 32 is an elevational cross-sectional view of the retractor of FIG.31, in the fully retracted position.

FIG. 33 is an elevational cross-sectional view of the retractor of FIG.31, at the commencement of the dispensation cycle.

FIG. 34 is an elevational cross-sectional view of a pneumatic platenretractor embodiment of the present invention.

FIG. 35 is a top plan view of the embodiment illustrated in FIG. 34.

FIG. 36 is a top plan view of a flexible platen retraction device inaccordance with the present invention.

FIG. 37 is an elevational cross-sectional view of the embodiment of FIG.36.

FIG. 38 is an elevational cross-sectional view of the embodiment of FIG.36, at the completion of the dispensation cycle.

FIG. 39 is an elevational cross-sectional view of the folding linkplaten retractor in accordance with the present invention.

FIG. 40 is an elevational cross-sectional view of the embodiment of FIG.39, with a retracting key in place.

FIG. 41 is an elevational cross-sectional view of the embodiment of FIG.39, at the commencement of dispensation cycle.

FIG. 42 is an elevational view of a linkage assembly.

FIG. 43 is an elevational view of an alternate linkage assembly.

FIG. 44 is an elevational cross-sectional view of an infusion pumphaving a drag element in accordance with the present invention.

FIG. 45 is an elevational cross-sectional view of an empty indicator inaccordance with the present invention.

FIG. 46 is an elevational cross-sectional view of the embodiment of FIG.45, at the completion of the dispensation cycle.

FIG. 46A is an enlarged portion of an elevational cross-sectional viewof the embodiment of FIG. 45, at the completion of the dispensationcycle.

FIG. 47 is a bottom plan view through the transparent window of theembodiment of FIG. 45.

FIG. 48 is a top plan view of a low-profile sliding spring retractorembodiment of the present invention.

FIG. 49 is a side elevational view of the embodiment of FIG. 48.

FIG. 50 is a side elevational view of the embodiment of FIG. 48, at thecommencement of the dispensation cycle.

FIG. 51 is a side elevational view of the embodiment of FIG. 48, partwaythrough the dispensation cycle.

FIG. 52 is a top perspective view of a scissor-type biasing means inaccordance with the present invention.

FIG. 53 is an elevational cross-sectional view of the embodiment of FIG.52.

FIG. 54 is an elevational cross-sectional view of the embodiment of FIG.52, at the completion of the dispensation cycle.

FIG. 55 is an exploded view of the embodiment of FIG. 52.

FIG. 56 is a plot of fluid pressure versus volume.

FIG. 57 is a plot of percent change in pressure versus volume.

FIG. 58 is a plot of fluid pressure versus volume.

FIG. 59 is a plot of percent change in pressure versus volume.

FIG. 60 is a plot of force versus volume.

FIG. 61 is a top plan view of the fluid container embodying the presentinvention;

FIG. 62 is a left side view of the fluid container of FIG. 61;

FIG. 63 is a front view of the fluid container of FIG. 61;

FIG. 64 is a rear view of the fluid container of FIG. 61;

FIG. 65 is a left side cross-sectional view of the fluid container ofFIG. 61 when full of fluid;

FIG. 66 is a top plan view of an alternative embodiment of the fluidcontainer shown in FIG. 61;

FIG. 67 is a left side view of the alternative embodiment shown in FIG.66;

FIG. 68 is a front view of the alternative embodiment shown in FIG. 66;

FIG. 69 is a rear view of the alternative embodiment shown in FIG. 66;

FIG. 70 is another alternative embodiment of the fluid container shownin FIG. 61;

FIG. 71 is a left side view of the alternative embodiment shown in FIG.70;

FIG. 72 is a front view of the alternative embodiment shown in FIG. 70;

FIG. 73 is a rear view of the alternative embodiment shown in FIG. 70;

FIG. 74 is a top plan view of another alternative embodiment of thefluid container shown in FIG. 61;

FIG. 75 is a left side view of the alternative embodiment shown in FIG.74;

FIG. 76 is a front view of the alternative embodiment shown in FIG. 74;

FIG. 77 is a rear view of the alternative embodiment shown in FIG. 74;

FIG. 78 is a top plan view of another alternative embodiment of thefluid container shown in FIG. 61;

FIG. 79 is a left side view of the alternative embodiment shown in FIG.78;

FIG. 80 is a front view of the alternative embodiment shown in FIG. 78;

FIG. 81 is a rear view of the alternative embodiment shown in FIG. 78;

FIG. 82 is a top plan view of another alternative embodiment of thefluid container shown in FIG. 61;

FIG. 83 is a left side view of the alternative embodiment shown in FIG.82;

FIG. 84 is a top plan view of another alternative embodiment of thefluid container shown in FIG. 61;

FIG. 85 is a left side view of the alternative embodiment shown in FIG.84;

FIG. 86 is a top plan view of another alternative embodiment of thefluid container shown in FIG. 61;

FIG. 87 is a left side view of the alternative embodiment shown in FIG.86;

FIG. 88 is a top plan, view of another alternative embodiment of thefluid container shown in FIG. 61;

FIG. 89 is a left side view of the alternative embodiment shown in FIG.88.

FIG. 90 is a perspective view of an alternative embodiment of the platenpump.

FIG. 91 is an exploded perspective view of the alternative embodimentshown in FIG. 90.

FIG. 92 is an exploded view of the scissor-type biasing means shown inFIG. 91.

FIG. 93 is a cut-away side view of the alternative embodiment shown inFIG. 90 with the platen in a first position.

FIG. 94 is a cut-away side view of the alternative embodiment shown inFIG. 90 with the platen in a second position.

FIG. 95 is a perspective view of the handle of the alternativeembodiment shown in FIG. 90.

FIG. 96 illustrates a scale on the alternative embodiment of the pumpshown in FIG. 90.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the figures, the infusion device of the presentinvention shall be called a platen pump. The platen pump is formed intwo parts, a pressurizing portion and a fluid containing portion. Eachportion is housed in a container or shell. A pressurizing shell 12includes a helical spring 14. A fluid containing shell 16 includes achamber 17 for housing a fluid delivery bag 18. When the pressurizingshell 12 and the fluid containing shell 16 are connected to form theenclosed pump, the fluid delivery bag is pressurized by the spring 14.Fluid is thus continuously forced out of the bag 18 through an outlettube 20 in fluid communication therewith. Controlled fluid flow isachieved with a small diameter fixed orifice 46 located at or near theend of the tube. The pump of FIG. 1 is 3 ½″ in diameter and 1.7″ high. Aselectively releasable clamp 34 may be applied to the outlet tube tostop fluid flow from the pump. Releasing the clamp restores fluid flow.

In accordance with the presently preferred embodiment of the invention,the pressurizing means is a conical helical coil spring 14. The springis formed from stainless steel or a suitable spring material. The coilsof the spring are made progressively larger so that when compressed thespring coils can overlap to compress to a lower height than aconventional compression spring. When the spring is expanded it takes ona conical shape. The conical helical spring exerts the greatest forcewhen it is fully compressed. The force is approximated by the equationF=kx, where k is the spring rate and x is the distance the spring iscompressed. Because it is desirable to have the force exerted on thedrug container be nearly the same when the container is full as when itis nearly empty, it is preferred that the free length of the spring beseveral times the height of the pump. Thus, the working length is but afraction of its total free length. This insures that the force appliedby the spring is kept within an acceptable tolerance from the beginningto the end of the infusion. In accordance with the presently preferredembodiment, the change in force exerted by the spring over the course ofan infusion as compared to the initial force it exerts when compressedagainst a full fluid delivery bag is less than ±20%. In accordance withthe invention, the spring length should be selected such that the changein force over the course of an infusion is less than 20%. In addition toa conventional compression spring, this concept would apply to a leafspring, if it was used instead, where the deflection in the leaf springis but a fraction of the total possible deflection.

A flexible cable retainer 26 encircles the spring 14 to set its initialcompressed height and also to prevent it from expanding beyond theheight of the pressurizing shell 12. In the presently preferredembodiment, two cables 26 are used. Thus, the spring 14 does not bearagainst the fluid delivery bag when the pressurizing shell 12 isinitially engaged with the fluid containing shell 16. This makes it easyfor a user to bring the two shells together. With the spring in itsinitially compressed state, the force differential between the fullposition shown in FIG. 4 and empty position with the bag squeezed to acompletely collapsed position is less than 20% of the initial force inthe full position. While the conical helical coil spring is preferred,it would be possible to make a platen pump with a leaf spring, apressurized bladder, a standard helical compression spring or a canisterof pressurized gas to act as the pressurizing means.

The smallest coil of the spring is rotatably attached to the closed endof the pressurizing shell 12. The spring is attached to the pressurizingshell by a rotatable connector including a spring retainer 22, an anchorpivot 28, a spring stop 23 and a screw 31. The anchor pivot 28 is seatedon a shoulder 29 encircling a hole in the top of the pressurizing shell12. The anchor pivot 28 is free to rotate on the shoulder 29. Therotatable spring retainer 22 is mounted to an anchor pivot 28. Thespring retainer 22 centers the spring to the shell. A spring stop 23clamps the end coil of the spring to the spring retainer and preventsthe spring from dislodging from the spring retainer 22. The screw 31holds the anchor pivot 28 and the spring stop 23 together. The springretainer 22 is sandwiched between the anchor pivot and the spring stop.

Preferably, in the present invention, a fluid delivery bag ispressurized to only about 5 psi which requires only about 30 pounds offorce. In order that health personnel or the patient can pressurize thepump without assistance, the pressurizing shell 12 and fluid containingshell 16 are threadably engaged. In the presently preferred embodiment,the pressurizing shell has inner helical threads 13 and the fluid incontaining shell has outer helical threads 19. By increasing the numberof threads per inch, the axial force provided by the threads can beincreased for a given torque. The presently preferred embodiment usesfour (4) threads per inch so that it is relatively quick and easy toscrew the shells together to fully pressurize the pump. The threadsprovide a mechanical advantages so that a modest amount of torque cangenerate sufficient amounts of axial load to compress the spring.

The platen 24 is located between the spring 14 and the fluid deliverybag 18 when the two shells are connected. The platen 24 distributes thepressure from the spring 14 over the bag. The presently preferred platenis made of polycarbonate. The platen has a bottom flat portion whichextends over an area no greater than a substantially flat centralportion of the full fluid delivery bag. This serves to keep thecontacting surface areas fairly constant over the course of the entireinfusion to help minimize changes in pressure on the fluid bag. Theplaten 24 is held against the helical coil within the pressurizing shell12 by the flexible restraining cable 26. The cable 26 is preferably madefrom multi-strand stainless steel. It is looped about the rotatableretainer 22 and the platen 24. Preferably, two cable loops 26 are used.Grooves are provided in the retainer 22 and platen 24 to accommodate thecables 26. A plastic label 36 may be adhered to the bottom of the platen24. The platen 24 and the cable 26 shell rotate freely about the axis ofthe pressurizing shell. Thus, when the pressurizing shell is rotatedwith respect to the fluid delivery shell to thread the two together, thepressurizing shell turns independently of the platen 24. The platen 24should remain stationary with respect to the fluid delivery bag so thatno torsional load is imparted on the bag. In order to mechanicallyprevent twisting the fluid delivery bag 18 when the two shells arescrewed together, anti-rotation tabs can be attached to the outer edgesof the platen 24. The tabs would extend out radially to engage slots inthe wall of the fluid containing shell 16. The tabs would be guided inthe slot, thus preventing the platen from turning with respect to thefluid containing shell. It has been found that rotatably attaching thespring and platen to the pressurizing shell is sufficient to avoidapplying undesirable torque to the fluid delivery bag. The tabs andslots are not required.

Because it is desirable to have a device which allows the patient toexamine the volume of fluid still retained in the fluid delivery bag sothat the patient can determine when the bag is empty, preferredembodiments of the present invention utilize a clear plastic window 38in the bottom of the fluid containing shell 16. Due to cost and safetyconsiderations, especially preferred embodiments of the presentinvention use a clear plastic, such as polycarbonate, as the windowmaterial. A legend such as the word “Empty” or “E” or some other symbolis embossed on the bottom side of the platen 24. Advantageously, thelegend will be fuzzy or illegible when viewed through the elastomericdisk and transparent window when there is liquid in the fluid deliverybag. When the bag has been emptied and the platen lies flat against thelayers of the bag, disk and the bottom of the chamber 17, the legend onthe platen 24 comes into focus through the bottom of the fluidcontaining shell due to the transparent nature of the fluid delivery bagand the contact clarity of the disk. This can be used to provide a clearindication of when the fluid bag is empty. It has been found that asmall amount of silicone oil between the window and the disk willenhance the clarity. Alternatively, a plastic label 36 may be adhered tothe bottom of the platen 24 having a legend thereon, as illustrated inFIG. 3.

To the extent possible, it is desirable to maintain a relativelyconstant flow rate throughout an infusion with the platen pump. In orderto minimize changes in the internal pressure within the fluid deliverybag, it is important that the surface area of contact between the bagand the rigid surfaces pressing against it be kept constant. Inaccordance with the present invention, the bottom of the chamber 17 inthe fluid containing shell 16 is contoured to evenly support the bottomof the bag over its entire area. Thus, the surface contact against thebottom of the bag remains constant during the full stroke of the platen.In the figures, a curved contour is shown about the periphery of thechamber 17. The bag 18 when filled with fluid matches this curvedcontour to receive support over its entire area. The contour of thechamber 17 could also be achieved with a 45° angle about the periphery.While the bag 18 might not completely fill the corner formed by theangle, the contour of the surface areas should be adequate to providesubstantial support and contact with the bag's entire area.

It is also important that the contact area of the platen 24 against thebag remain constant. Therefore, the platen 24 has a bottom flat surfacewhich does not extend beyond a flat central portion of the fluiddelivery bag. If only the flat portion of the platen were to act on thebag, a residual fluid would remain in the bag about its periphery at theend of the infusion. In order to more completely deliver the fluid fromthe bag, the platen has a chamfered edge 40 and a recessed outer ring42. These portions of the platen roughly match the contour of theperiphery of the bottom of the chamber 17. A platen 24 with a peripherythat conforms more exactly to the contour of the chamber bottom couldalso be used. Near the end of an infusion, as the platen 24 descendstowards the chamber bottom, fluid which builds up about the periphery ofthe bag 18 is pushed out by the edge 40 and the recessed ring 42.

An opening 30 is provided in the fluid-containing shell through whichthe outlet tube connected to the fluid delivery bag 18 can be extended.An outer wall 32 of the fluid containing shell can be provided to serveas a grip. When screwing the shells together, one hand holds the outerwall of the pressurizing shell and the other hand holds the outer wall32 of the fluid containing shell 16.

These two shells of the pump are circular in shape to permit threadableengagement. Referring now to FIG. 7, the fluid delivery bag 18 for usein the platen pump is a circular pouch connected to an outlet tube. Thecircular pouch, advantageously, has no corners. Thus, the seam 44 of thebag is uniformly stressed. To assist in achieving uniformity of pressurein the bag, the periphery of the bag has a curved contour when filled.The center portion of the bag is substantially flat so that thecontacting surfaces between the platen and the bag can remain relativelyconstant throughout an infusion. The bag is made from a suitable pliablebiocompatible plastic material, such as a class VI, PVC biocompatibleplastic. The bag is formed from two sheets that are RF welded togetherand trimmed around their circumference. The round shape of the bagachieves uniform stress on the welded seam.

The outlet tube 20 is connected to the bag 18. The tube 20 may lead to arestricted orifice 46 which restrains the flow of fluid from thedelivery bag when it is pressurized. Orifices of 0.004″ to 0.008″diameter are presently contemplated. In order to prevent the orificefrom becoming blocked, an optional particulate filter 48 can be insertedin the outlet tube to stop the flow of particles which might occlude theorifice. The orifice provides a relatively constant fluid flow. As analternative to the restricted orifice, a length of tubing of knowndiameter, e.g., an 18 inch length of 0.015″ tube can be substituted. Inorder to facilitate filling the fluid delivery bag, a Y-injection site52 may be inserted into the outlet tube 20. The Y-injection site 52includes a latex rubber self-sealing septum 54 through which a needlemay be inserted to inject fluid into the bag. As an alternative, asecond filling port (not illustrated) may be added to the bag.

The end of the outlet tube can be connected to a luer adapter 50, Theadapter is a threadably engaged connector. It is designed to mate with athreadably engaged disconnect on an IV line. In order to permitreusability of an infusion set, the outlet tube 20 of the fluid deliverybag can be directly connected to a second luer adapter 50 (notillustrated) approximately 3 inches from the drug bag. A clamp would beused on the tube between the bag and the luer adapter 50. Fluid may beinjected in through the luer adapter 50 so a Y-injection site would notbe needed. When the drug has been expended, a new drug bag may beattached to the IV set, thus reusing the IV set for multiple doses overa 24 to 48 hour period.

In practicing the invention, the clamp 34 is used to close the outlettube on an empty drug delivery bag. A needle pierces the septum 54 toinject fluid into the drug delivery bag. The bag when full should have asubstantially flat top and bottom central portion when resting on a flatsurface. The needle is removed. The bag, with its permanently affixed IVline, is placed in the chamber 17 of fluid containing shell 16 with theIV line passing through the opening 30 in the bottom of the shell. Whenthe upper and lower shells are brought together, the threads shouldpreferably engage initially before the platen 24 pressurizes the bag.The two shells are then simply screwed together until a stop position isreached. At this point, the drug bag is fully pressurized. The IV outputline is purged of air by opening the clamp 34 and allowing fluid toflow. Once the fluid stream ejects slightly, the tube can be reclamped.The output line is then connected to a catheter line or needle foradministering an infusion to a patient. Releasing the clamp initiatesfluid flow. When the legend on the platen 24 comes into focus throughthe window 38 in the fluid containing shell 16, the bag has beenemptied. The output line is removed or disconnected from the patient.The two shells are then unscrewed and the drug container and IV line arediscarded. The pump can be reused.

Referring now to FIGS. 8, 8 a and 8 b, an alternate embodiment of thepresent invention illustrated. The numerical labels in the drawings are100 higher than corresponding similar elements in the first embodiment.When it is desired to use a conventional rectangular drug delivery bag118, the alternate embodiment can be used. The fluid containing shell116 of the alternate embodiment is provided with a rectangular chamberto accommodate the rectangular drug delivery bag. The fluid containingshell 116 is formed by an upper portion 152 and lower portion 154attached at one end by a hinge 156. The opposite ends are connected by alatch 158 when the upper and lower portions are closed. The upperportion 152 includes a threaded cylindrical wall 119 for interfacingwith the threaded wall 113 of the pressurizing shell 112. The platen 124attached to the spring 114 of the pressurizing shell 112 is maderectangular to fit over the substantially flat center portion of therectangular bag. In this embodiment, the delivery bag 118 has an outlettube with a fitting 121 thereon for coupling to a fluid line. Inaddition, the platen 124 has an outer diameter which is larger than theinner diameter of the pressurizing shell 112, whereby the upward travelof the platen 124 is limited. In this arrangement, the platen 124 movesfrom a first position in which its outer flange abuts the shell 112(when the bag is full) and a second position nearer the lower portion154 when fluid is expelled from the bag.

To operate the platen pump of the alternate embodiment, the pressurizingshell is unscrewed and loosened on the fluid containing shell. The fluidcontaining shell is opened about its hinge or sliding means. A fluiddelivery bag is inserted. The fluid containing shell is closed at itslatch. The pressurizing shell can then be screwed onto the fluidcontaining shell to pressurize the drug delivery bag.

In accordance with a further aspect of the present invention, there isprovided an infusion pump having a platen which is divided into two ormore segments. Preferably, each segment is provided with an independentbiasing means for compressing each respective segment against themedication bag. The multi-segment pressure pad of the present inventioncooperates with the changing contour of the deflating medication bag tomaintain an improved relatively constant surface contact area betweenthe platen and the bag. As has been previously discussed, themaintenance of a substantially constant surface contact area has beendetermined by the inventors herein to promote constant output pressureperformance.

Referring to FIGS. 9-12, there is disclosed a dual concentric platenembodiment of the infusion pump in accordance with the presentinvention. Infusion device 160 is provided with a housing 162,comprising a cover portion 164 and a base 166. As with previousembodiments, the cover 164 and base 166 are preferably formed inaccordance with conventional techniques for the production of medicaldevice housings, such as injection molding of thermoplastic or thermosetpolymers. Alternatively, any of a variety of other techniques may beutilized, including fabrication from sheet metal stock, as will be wellunderstood by one of skill in the art.

The cover 164 and base 166 can be secured together in any of a varietyof manners disclosed elsewhere herein. For example, cover 164 and base166 can be provided with complementary surface structures such as maleand female engaging threads. For this purpose, base 166 is provided withan annular, axially extending wall 170 to provide an extended surfacecontact area between the base 166 and cover 164. Alternatively, thecontacting surfaces of the cover 164 and base 166 are provided withcomplimentary pins and J- or L-shaped grooves to permit apress-and-twist fit interlock. Any of a variety of alternativeinterlocking structures may be utilized with the multiple segment platenembodiment of the invention.

Depending upon the type of spring retraction structure utilized, thebase 166 and cover 164 may or may not need to be removably connected.For example, in a side loading embodiment, base 166 and cover 164 may beintegrally formed or permanently secured together during themanufacturing process. In this embodiment, an opening is provided in theside wall to permit introduction of a medication bag between theretracted platen and base as will be discussed.

In general, base 166, annular wall 170 and cover 164 cooperate to form achamber 172 for containing the functional components of the infusiondevice 160. In the illustrated embodiment, a first platen segment 176 isbiased against a medication bag 174 by means of a coil spring 178.Platen segment 176 is provided with an axially extending spring guide184, which may comprise an axially extending annular wall or a pluralityof axially extending projections. Spring guide 184 assists inmaintaining the axial alignment of the spring 178 during repeatedtensioning and discharge cycles of the infusion device 160. The springguide 184 may alternatively be positioned on the radially interior sideof spring 178, as well as on the radial exterior or radial interior sideof the spring but depending from cap 164, as will be apparent to one ofskill in the art.

The first platen segment 176 is provided with a radially outwardlyextending annular flange 186 for cooperating with a radially inwardlydirected stop 188 on second platen segment 180. Stop 188 is axiallyspaced apart from the plane of second platen segment 180 by a support190, as will be discussed.

Second platen segment 180 comprises an annular ring positionedconcentrically about the first platen 176. Second platen 180 isindependently axially movable with respect to first platen 176, andmoveable from a first position spaced apart from the plane of firstplaten segment 176 to a second position substantially in the plane offirst platen segment 176. Preferably, second platen segment 180 isbiased in the direction of medication bag 174 by a second spring 182.

Although first spring 178 and second spring 182 are illustrated assubstantially cylindrical in configuration, a conically shaped spring isalso desirable for the reasons previously discussed. In addition,alternative biasing means such as leaf springs, pressurized bladders,canisters of pressurized gas or the like may also be adapted for use inaccordance with the multi-segment platen embodiment of the presentinvention.

The illustrations contained in FIGS. 9-11 are simplified somewhat tohighlight the multiple platen aspect of the invention. However, avariety of additional features will generally be incorporated into afinished device. For example, a spring or platen retraction structurefor retracting the platen and limiting the distention of the spring inthe absence of a base 166 or fluid bag 174 is also typically used. Avariety of suitable retention structures are disclosed elsewhere herein,or will be immediately apparent to one of skill in the art in view ofthe present disclosure. In a side loading-type embodiment, a springretraction structure is particularly desirable.

Fluid bag 174 is in fluid communication with the patient by way ofeffluent fluid line 168. Fluid line 168 extends through the housing 162by way of a port 169. Modification of the port 169 to accommodate thevarious relationships between the cover 164 and base 166 will beapparent to one of skill in the art. Alternatively, in a side loadingembodiment of the multiple segment platen pump, the port 169 ispreferably configured in the form of a circumferentially extending slothaving a wide enough opening in the circumferential and axial directionsto accept the appropriately sized fluid bag 174.

In general, the fluid bag diameters contemplated for use in accordancewith the present invention are in the area of from about 3.5 inches indiameter to about 5 inches in diameter, and from about 0.5 inches toabout 1.0 inches thick. However, infusion pumps adapted to receive othersized bags can be readily produced in accordance with the disclosureherein.

FIG. 10 illustrates the configuration of the pump with a relatively fullmedication bag 174. Second platen 180 compresses the radiallyexterior-most portion of bag 174 independently of the first platen 176,which provides pressure against the central portion of bag 174. It hasbeen determined that the provision of this bifurcated biasing allows asurprisingly more constant pressure output profile compared to the useof a planar single flat platen design.

FIG. 11 illustrates the configuration of the device when the medicationbag 174 is approximately one-half empty, and FIG. 12 illustrates thedevice when the fluid medication bag 174 has been substantiallycompletely emptied.

In a dual segment platen embodiment designed for use with a 3.5-inchdiameter, ½ inch thick 50 cc medication bag 174, the first platen 176has a circular contact surface having a diameter within the range offrom about 2.2 to about 2.8 inches. The bag contact surface on secondplaten 180 is in the form of an annular ring, with the width of the ringat any one point being within the range of from about 0.4 to about 0.7inches. The overall outside diameter across the entire second platen 180is approximately equal to the exterior diameter of the bag.

The relative extent to which the second platen 180 can travel distallyalong its path of travel with respect to the first platen 176 is limitedby the axial height of the support 190. In an embodiment having a bagwhich is approximately one-half inch thick when full, the length of thesupport 190 is about 0.4 inches.

In accordance with a further aspect of the present invention, there isdisclosed an alternate multi-segment platen embodiment at FIGS. 13-17.Referring to FIG. 13, infusion pump 192 comprises a housing 194 havingan upper wall 196 and lower wall 198. Upper wall 196 and lower wall 198may be rigidly secured with respect to one another, or removably securedwith respect to one another such as by threadable engagement or otherpreviously disclosed means.

Upper wall 196 can be substantially planar throughout the width of thepump 192, or, as illustrated in FIGS. 13-15, can have a substantiallyplanar central region and a sloped annular region 197. Sloped region 197is provided on the interior surface with a peripheral spring guide 211,which is preferably an integrally molded annular ring.

A chamber 200 is formed between upper wall 196 and lower wall 198 toreceive the functional components of the infusion pump 192. A platen 202is movably disposed between upper wall 196 and lower wall 198. Platen202 comprises a central region 204 and a peripheral region 206.Referring to FIG. 16, a multi-segment peripheral region 206 isillustrated.

Central region 204 is biased in the direction of lower wall 198 by atleast one central spring 208. Central spring 208 is preferablymaintained in position with the assistance of central spring guide 209,which may comprise a plurality of axially extending projections or anannular ring. Alternatively, spring 208 can seat within an annularrecess disposed on the spring side of central region 204 of platen 202.

The peripheral region 206 is biased in the direction of lower wall 198by one or more peripheral springs 210. Although each of the peripheralsegments 214 can be provided with independent biasing means, a singleannular peripheral spring 210 has been determined to performsatisfactorily in embodiments of the present invention.

An approximation of the deflation cycle is illustrated in FIGS. 13-15.At the completion of the infusion cycle, the platen 202 is biasedagainst the lower wall 198 to substantially completely expel all of thecontents of the fluid bag. In this embodiment, the lower wall 198 isprovided with an axially upwardly inclined peripheral zone 199, which isdimensioned to be complementary with the peripheral region 206 on platen202.

Referring to FIG. 16, each of the peripheral segments 214 on platen 202is connected to the central region 204 by way of a hinge 215. Hinge 215can be provided in any of a variety of ways, and still accomplish theobjectives of the present invention. For example, the entire platen 202can be formed from a sheet of material having sufficient flexibilitythat the biasing forces due to central spring 208 and peripheral spring210 will deform the platen, as illustrated in FIG. 14. Preferably,however, the hinge 215 comprises a relatively more flexible zone thanthe surrounding material of platen 202. This may be provided, forexample, by reducing the thickness of the platen material in the regionof each hinge 215, as illustrated, for example, in FIGS. 13-15.Alternatively, the central zone 204 can be formed separately from theperipheral segments 214, and assembled thereafter such as by mountingthe central zone 204 and peripheral segments 214 on a flexible sheet ofmaterial, reduced thicknesses can be produced by injection molding ofthe platen. Any of a variety of stamping and/or milling or grindingtechniques may also be utilized to produce an annular groove in thematerial of an integrally formed platen 202.

Referring to FIG. 17, there is disclosed an alternate embodiment of theplaten 202, particularly adapted for an infusion pump designed for usein an octagonal housing.

Spring rates and lengths may be selected to complement the respectivesurface areas of the central and peripheral zones to achieve the mostacceptable internal bag pressure.

Referring to FIGS. 18-20, there is disclosed a leverage assisted springretractor for loading an infusion pump 216 in accordance with thepresent invention. The spring retractor is conveniently operated by apatient actuated lever, to retract the platen against the spring biasinto the “ready” position. The fluid medication bag may thereafter beeasily inserted either through a side opening on the device or byremoving the bottom shell.

Referring to FIG. 18, infusion pump 216 is provided with a springretractor 218. Spring retractor 218 is operated by lifting a patientactuated lever 220, which rotates about a fulcrum 222 on the housing ofthe infusion pump 216. The lever 220 extends through an opening 223 intothe upper housing 232, and is thereafter provided with a ramp 224 suchas a cam or other structure having a surface for slidably engaging a pin230. The pin engaging surface of ramp 224 is preferably provided withfriction enhancing surface structures such as a plurality of teeth 225.In this manner, the lever can be released by the patient at any pointthroughout its range of travel, and the teeth 225, pin 230 and curvatureof ramp 224 cooperate to retain the partially retracted lever inposition.

Pin 230 is connected to a support 228 for transferring force to theplaten 226. Although illustrated as a unitary platen 226, the springretractor in accordance with this aspect of the present invention can bereadily utilized with the dual platen embodiment which has previouslybeen disclosed.

To facilitate lifting of the lever 220, the lever 220 extends slightlybeyond the outer periphery of the housing 232 to provide a tab 221.Alternatively, any of a wide variety of friction enhancing or grippingsurface structures can be provided, as will be apparent to one of skillin the art.

In addition, the cam configuration is preferably such that the lever 220has a minor amount of free play before the friction enhancing structures225 engage the pin 230. In this manner, the lever 220 can be readilylifted slightly away from the upper housing 232 so that the patient caneasily position fingers underneath the lever 220 before retracting thelever against the resistance provided by spring 231.

The spring retractor 218, in accordance with the present invention, canbe utilized with any of a variety of housing structures. For example, inthe embodiment illustrated in FIGS. 18-20, the housing comprises anupper housing 232 removably secured to a lower housing 234 by way of aplurality of threads 236. When the lower housing 234 is threadablyremoved from the upper housing 232, the combination of the ramp 224, pin230, support 228 and platen 226 operate to limit the expansion of thespring to retain the desired prestressing. Thus, the housing can bedisassembled with the platen either in the extended or retractedpositions, and a fluid medication bag 235 can be placed within the lowerhousing 234.

Since reassembly of the lower housing 234 with upper housing 232 is notopposed by any force from the spring 231, any of a wide variety ofsecuring means can be utilized in place of the illustrated threads 236.For example, snap fit structures, hinge and latch arrangements, and thelike can be readily adapted for use. Alternatively, side installationembodiments are also contemplated by the present inventors. For example,the upper housing 232 and lower housing 234 can be integrally molded, orcan be secured together in a permanent fashion following installation ofthe functional components. A port (not illustrated) on the side of thehousing is then appropriately sized to receive a fluid medication bag235 therethrough.

The embodiment illustrated in FIGS. 18-20 provides a uniquely lowprofile infusion pump 216, which may be readily loaded by the patientwithout the use of any additional tools, and which has a thickness ofonly slightly greater than the sum of the inflated medication bag andthe length of the collapsed spring.

FIGS. 21-24 illustrate a key operated platen retractor in accordancewith a further aspect of the present invention. Referring to FIG. 21,there is disclosed an infusion pump 238 having a key operated platenretractor 240 thereon. Platen retractor 240 comprises a threaded member242 such as a disk, which is connected to the platen 244 by way of aspacer 246. As will be appreciated by one of skill in the art, thethreaded element 242 may comprise either a disk having an externalthread on the circumferential surface thereof, or an aperture boredaxially through spacer 246 and provided with a female thread forreceiving a threaded key.

Referring to FIG. 22, a key 248 is provided for threadably engaging thethreaded disk 242. Key 248 is provided with an aperture extendingtherethrough, and having a female thread thereon.

Threaded disk 242 operates as a stop by abutting against a portion ofthe housing, thereby limiting axial expansion of the spring. In thismanner, the spring can be prestressed as desired.

Preferably, the threaded disk 242 is axially movably positioned within awell 250. Well 250 serves multiple functions, including permitting theloaded infusion pump 238 to retain the same exterior profile as thedischarged infusion pump 238, as illustrated in FIGS. 23 and 21,respectively. In addition, the lower limit of the well 250 operates as astop to prevent further expansion of the spring. Additionally, threadeddisk 242 can serve as a liquid level indicator.

In use, the user inserts the key 248 into the well 250, and rotates thekey to engage the threads on disk 242. Continued rotation of the keydraws the disk axially against the bias provided by the spring, untilthe platen is in the fully retracted state. When fully retracted, theplaten abuts the lower wall of the recess 250, as illustrated in FIG.22. At this point, the lower portion of the housing can either beremoved for installation of a fluid medication bag, or the fluidmedication bag can be installed through a lateral or side entry port. Itis therefore preferable that the distance between the platen when fullyretracted and the bottom of the housing be slightly greater than thethickness of the filled medication bag, so that the bag may beconveniently slidably positioned therebetween.

Once the bag is in position, the user simply reverses the direction ofrotation of the key, and spins the key to remove it from the threadeddisk 242. Once the key is partially backed off of the threaded disk 242,the medication bag will be under pressure exerted from the platen 244.

Referring to FIG. 24, there is disclosed a loaded and pressurized fluidmedication delivery pump 238, similar to that illustrated in FIGS.21-23, and including some additional details. For example, thecross-sectional view of the threads 252 reveals that the thread has awidth which changes from a relatively narrow dimension at the point ofattachment of the thread to the corresponding support structure, to arelatively wide width at the free end of the thread. Similarly, thechannel for receiving each thread is provided with side walls whichtaper towards each other in a direction extending away from the bottomof the channel. In this manner, the threads are provided with a full orpartial interlocking fit, which will permit the use of thinner, moreflexible construction materials for the side walls of the housing, whileminimizing the risk that plastic deformation of the side walls underbias from the spring will cause the threaded side walls to disengagefrom each other.

In addition, an annular platen guide 253 is provided to optimize theprecision of the axial travel of the platen 244 throughout thedispensation and reloading cycles. Platen guide 253 cooperates with anannular spring guide 254. Platen guide 253 and spring guide 254 in onepreferred embodiment comprise concentric annular flanges which areaxially movable towards and apart from each other in a telescopingfashion.

An alternate means for connecting the spacer 246 to the platen 244 isalso disclosed in FIG. 24. Although the spacer 246 may be integrallymolded or otherwise formed with the platen 244, the spacer 246 may, formanufacturing reasons, preferably be separately manufactured and laterconnected to the platen 244. This may be convenient from a manufacturingstandpoint or because of the desirability to utilize differentconstruction materials for the platen and the spacer 246.

For example, referring to FIG. 24, the spacer 246 extends through anaperture in the platen 244. A shallow recess 249 is provided on themedication bag side of the platen 244, and preferably is radiallysymmetrically disposed about the axis of the spacer 246. Recess 249receives an anchor 247 on the end of spacer 246. Anchor 247 may be anintegrally formed disk or sheet on the end of spacer 246. Alternatively,anchor 247 is secured to spacer 246 in a post-forming operation, such asby spot welding, solvent bonding, thermal bonding, or attachment byscrews or other fastening means.

In a preferred embodiment, the threaded disk 242, spacer 246 and anchor247 are all manufactured from a suitable non-corrosive metal such asstainless steel to minimize the occurrence of stress fatigue followingrepeated usage of the infusion pump 238. As illustrated in FIG. 24,anchor 247 is preferably seated within recess 249 in such a manner thata smooth exterior surface is provided for compressing the fluidmedication bag.

The overall thickness of the infusion pump 238 can be reduced byincorporating a collapsible platen retractor and restrainer. Forexample, referring to FIGS. 25 and 26, there is disclosed an infusionpump 256 having a collapsible platen retractor 258. Collapsibleretractor 258 generally comprises a first segment 260 which is axiallymovably disposed with respect to a second segment 262. The first segment260 and second segment 262 are assembled in such a manner that theyoperate to limit the distal travel of the platen as illustrated in FIG.26. In this manner, the base of the infusion pump can be removed, and amedication bag inserted therein, while the collapsible platen retractor258 retains a prestress on the spring.

In the illustrated embodiment, first segment 260 is convenientlyprovided in the form of a tubular body 261 having a longitudinal axiswhich extends at a perpendicular to the plane of platen 268. The tubularbody 261 of first segment 260 may be integrally molded with the platen268, or secured thereto using conventional techniques sufficient towithstand the forces generated by the spring for any given embodiment.The proximal end of the tubular body 261 of first segment 260 isprovided in the illustrated embodiment with a radially inwardly directedflange 263 which operates as a limit on travel with respect to secondsegment 262, as will be discussed.

Second segment 262 in the illustrated embodiment comprises an elongatebody portion 264 having a first end 265 and a second end 266.Preferably, first end 265 comprises a transverse element, such as adisk, extending generally in a plane which is transverse to thelongitudinal axis of body 264, and adapted for reciprocal axial motionwithin a recess 267 provided on the housing of infusion pump 256. Therecess 267 terminates in a stop such as a radially, inwardly directedannular flange 269 for limiting travel of the disk shaped first end 256.See FIG. 26.

Similarly, the second end 266 of body 264 is provided with anenlargement for cooperating with the flange 263 on tubular body 261 tolimit the extension of the platen 268. Thus, second end 266 proximallycomprises one or more barbs having a ramped distal surface, and aproximally facing shoulder to cooperate with flange 263 as isillustrated in FIG. 26. In this embodiment, second end 266 is generallyin the second form of a rounded screw head, having a slot 270 extendingaxially therein. This design permits easy assembly of the components ofthe invention, such that the second end 266 can be press fit through theopening within annular flange 263, to provide an axially movablyinterlocking fit between first segment 260 and second segment in theembodiment

Retraction of the platen 268 against the spring bias in the embodimentillustrated in FIGS. 25-26 can be accomplished in any of a variety ofways disclosed elsewhere herein. For example, first end 265 can beprovided with an exterior thread, for threadably receiving a key such asthat illustrated in FIG. 22. In this manner, first end 265 can be drawnaxially against the direction of force generated by the spring, toretract platen 268 to the position illustrated in FIG. 25. At that time,a medication bag 272 is inserted into the pump 265 such as by insertionthrough a lateral opening, or by removal of the base of the pump 256.Following introduction of the medication bag 272, the key (notillustrated)is removed form the first end 265. As illustrated in FIG.25, the second segment 262 can thereafter be slidably collapsed withinthe tubular body 261 of first segment 260, to provide a sleek exteriorprofile of the infusion pump 256.

Alternatively, any of the additional retraction structures disclosedherein can also be incorporated into the present embodiment

Referring to FIGS. 27-29, there is disclosed an ultra-flat springpowered pump comprising at least one spring 274, positioned within ahousing 276 for biasing a platen 277 against a base wall 278 forcompressing a fluid medication bag therebetween. Platen 277 is retractedagainst the force of the spring 274 by a rotatable retraction mechanism279.

Preferably, retraction mechanism 279 comprises a threaded shaft 280which is rotatably linked to platen 277. This is convenientlyaccomplished by providing a radially enlarged anchor 289 on the end ofshaft 280 and positioning shaft 280 through an opening in platen 278which is too small to permit passage of anchor 289, as illustrated.

The proximal end of shaft 280 is adapted to receive a crank 281 topermit the patient to rotate the threaded shaft 280 to retract platen277. In the illustrated embodiment, an opening in the upper portion ofthe housing is provided with a complementary female threaded surface forcooperating with the threads on threaded shaft 280.

In this embodiment, the platen 277 is retracted by rotating the threadedshaft 280 so that a medication bag 282 can be installed between theplaten and the base. Thereafter, in order to reduce the profile of thepump, the threaded shaft 280 may be rotated in a reverse direction toadvance fully or partially axially back into the medication bag 282 asillustrated in FIG. 29. For this purpose, medication bag 282 preferablycomprises a material which will permit the flexible deformationillustrated in FIG. 29, and the volume of fluid contained in themedication bag 282 should be sufficiently low in relation to the elasticlimit of the bag, to accommodate the displacement illustrated in FIG.29.

Referring to FIG. 30, there is disclosed an end elevational view of aninfusion pump such as that illustrated in FIGS. 27-29. As illustratedtherein, a scale 283 provides an indicium of the relative status of thepump throughout the dispensation cycle. In the illustrated embodiment,the platen 277, or an extension of the platen 277 is visible through anopening 284 on the side of the housing. Status indicium 285 are providedon the side of the housing for allowing the user to roughlyquantitatively evaluate the remaining portion of the dispensation cycle.

For example, in the illustrated embodiment, the scale 283 runs from 100to zero. This scale may represent the percentage of remaining medicationin the bag. Alternatively, in a device which is dimensioned toaccommodate a 100 cc delivery bag, the scale could indicate remainingmilliliters of medication. In an embodiment having a single, known flowrate and medication volume, the indicium 285 can be provided in units oftime such as hours or minutes, reflecting the remaining time of thedispensation cycle.

Also illustrated in FIG. 30 is an alternative crank arrangement forretracting the platen 277. Crank 286 is pivotally attached to threadedshaft 280, so that it can be conveniently moved from a first compactposition 287 such as during storage or use, to a second ready position288 in which the crank is positioned for use in retracting the platen277.

Referring to FIGS. 31-33, there is disclosed an alternate embodiment ofan infusion pump having a collapsible, segmented, platen retraction andretention structure. This embodiment permits the use of a threadedretractor such as that illustrated in FIGS. 27-29, yet permits thethreaded retractor to be reinserted into the pump to provide a generallysmooth exterior configuration, without indenting the medication bag.

Referring to FIG. 31, a first segment 290 preferably comprises athreaded post which engages complementary threads in an opening in thetop of the pump housing, so that rotation of the threaded post draws thepost axially through the opening of the housing. First end 292 andsecond end 293 of first segment 290 are provided with an enlargementsuch as a disc-shaped stop, for reasons which have been previouslydiscussed, for example, in connection with the embodiments illustratedin FIGS. 25-29. Similarly, second segment 291 preferably comprises atubular element analogous in structure and function to the segment 260illustrated in FIG. 25. In either embodiment, however, a variety ofalternative structures for retracting and restraining the platen such asonly partially indenting the medication bag, will be apparent to thoseof skill in the art in view of the disclosure herein.

Referring to FIG. 32, rotation of the threaded shaft 290 draws theplaten against the bias provided by the spring, to produce an openingfor receiving a fluid medication bag. In the illustrated embodiment, twocoil springs are illustrated in cross section. However, anywhere fromabout one to about five or more springs can readily be incorporated intoa design of the present invention.

Threaded post 290 can be rotated using any of a variety of implements,such as an ALLEN WRENCH or similar multi sided tool, a crank, arotatable nut, an electric drill, or others as will be apparent to oneof skill in the art.

The dimensions of the embodiment illustrated in FIGS. 31-33 can bevaried throughout a considerable range, depending upon the desiredvolume of medication to be infused in a given dispensation cycle, aswell as other considerations that will be apparent to one of skill inthe art. In general, however, the thickness of the pump along an axisparallel to the longitudinal axis of the spring is preferably no thickerthan about 2 inches, and more preferably within a range of from about1.4 inches to about 1.6 inches in an embodiment adapted for receiving a0.5-inch thick medication bag. In this embodiment, the distance betweenthe retracted platen and the base is preferably about 0.6 inch, topermit sufficient clearance to easily install a medication bag.

Preferably, as discussed in connection with FIGS. 27-30, the edge of theplaten is visible through the opening 294 or other window to permit theuser to assess the remaining fluid volume in the medication bag.

Retraction of the platen in order to facilitate introduction of amedication bag can alternatively be accomplished through any of avariety of hydraulic or pneumatic means. For example, referring to FIGS.34 and 35, there is provided a pneumatic lift for moving the platen froma second distended position to a first retracted position to facilitateintroduction of a medication bag. In this embodiment, there is providedone or more pneumatic cylinders 296 for advancing the platen against thebias provided by one or more springs 297. Pneumatic cylinder 296generally comprises a housing 298 for defining a chamber 299, having atleast one movable wall 300 axially slidably disposed within the housing298 to enlarge or contract the volume of chamber 299. Movable wall 300is mechanically linked to platen 302 by a spacer 301. Movable wall 300is provided with any of a variety of known sealing rings or other meansfor providing a seal between the movable wall 300 and housing 298.

At least one port 303 is provided on the housing for communicating withthe chamber 299. In operation, a source of a pressurized material suchas a fluid or gas is placed in communication with port 303 and forcedinto chamber 299 under sufficient pressure to advance wall 300 againstthe force resulting from one or more springs 297.

In a preferred embodiment, two or more pneumatic cylinders 296 areprovided. Thus, for example, there is disclosed in FIG. 35 a top planview of an infusion pump having seven pneumatic cylinders 296 positionedabout the periphery of a medication bag. To facilitate retraction of theplaten by infusing pressurized fluid or gas through only a single port303, each of the chambers 299 of the pneumatic cylinders 296 are incommunication with each other by way of a flow path 304.

In accordance with one embodiment, four pneumatic cylinders 296 areprovided, each having an internal diameter of about one-half inch. Thisprovides a surface area on movable wall 300 of approximately 0.196square inches per pneumatic cylinder, for a total of 0.784 square inchesfor the set of four. To provide a lift of 150 pounds, assuming nofriction, a fluid will need to be introduced into port 303 atapproximately 190 psi. By doubling the piston area to 1.57 squareinches, such as by providing eight pistons instead of four, the requiredpressure of the pneumatic fluid drops to about 95 psi. A variety ofpressure sources can be utilized, as is discussed infra.

Alternatively, referring to FIGS. 36-38, there is disclosed a pneumaticretraction embodiment in which one or more flexible bladders areutilized to provide the force necessary to retract the platen againstthe spring bias. Thus, referring to FIG. 36, there is disclosed a topplan view of an embodiment of the present invention having two elongatetubular bladders 306 in communication with a fill port 308 by way oflumen 307. As illustrated in FIGS. 37 and 38, inflation of the bladders306 advances the platen against the spring bias provided by one or moresprings 309 to provide sufficient space between platen 310 and base 311to accommodate a fill medication bag 312.

Any of a variety of configurations for bladder 306 may be utilized inaccomplishing the present embodiment of the invention. In general, thebladder comprises one or more elongate tubular bodies having a diameterwhich is sufficient in its inflated state to provide a sufficientdistance between the platen 310 and base 311 to accommodate themedication bag 312. The axial length of the bladder 306 will depend uponthe size of the medication bag contemplated, together with factors suchas the maximum acceptable pump housing size, and the maximum acceptablepressure required to retract the platen. In general, the larger volumeof bladder 306 will enable the use of less compressive force to retractthe platen, but will require a larger housing as will be apparent to oneof skill in the art.

Motive force for filling the bladder 306 can be provided in any of avariety of ways, utilizing either a fluid or a gas medium. For example,the fill port 308 can be provided with a luer connector or otherconventional means for establishing fluid communication with aconventional syringe having a volume sufficient to inflate the bladder306. The syringe may be filled with water, or air, depending upon therelative force characteristics of the bladder and spring. In thehospital or clinical setting, pressurized air from a house compressionsystem, such as is commonly available through a wall outlet in thepatient's room, can be utilized. Alternatively, compressed CO₂cartridges or other convenient sources of pressurized air or liquid canbe readily utilized.

Referring to FIGS. 39-41, there is disclosed a further embodiment of theinfusion pump in accordance with the present invention. In thisembodiment, retraction of the platen is accomplished by the use of athreaded key, as has been previously discussed, and the overallthickness of the infusion pump is minimized through the use of a foldinglink lift mechanism.

In this embodiment, infusion pump 314 is provided with one or moresprings 320 for biasing a platen 316 in the direction of base 318, ashas been previously discussed. In order to limit the distal travel ofplaten 316, such as when the base 318 is removed, and to retract theplaten 316 against the bias provided by spring 320, a retraction andretention structure 322 is provided.

Referring to FIG. 42, the retraction and retention structure 322generally comprises a folding linkage assembly 324. The linkage assembly324 permits the relative movement of proximal end 325 and distal end 326between a first position in which proximal end 325 and distal end 326are spaced apart by a predetermined maximum distance, and a secondposition in which proximal end 325 and distal end 326 are spaced apartby a lesser distance.

In the embodiment illustrated in FIG. 42, linkage assembly 324 isprovided with a first segment 327, which is pivotably secured to theproximal end 325 such as by a pin 328. The distal end of linkage 327 isprovided with a slip joint connection with a second linkage 329. Theslip joint connection is conveniently accomplished by providing one ofthe first and second linkages with an axially extending slot, and theother of the first and second linkages with a pin 332 for extendingthrough the slot, together with an anchor such as a nut, soldered washeror pin for preventing removal of the pin 332 from the slot.

The second linkage 329 is thereafter pivotably connected to the platen316, such as by providing a proximally extending flange on the platen316 for pivotally engaging the distal end of the second linkage 329.

Preferably, this embodiment is provided with a threaded plug at theproximal end 325 of folding linkage 324, adapted to be received within akey 330, as has been discussed in connection with previous embodiments.Alternatively, other retraction structures such as a lever can also beused in the present embodiment. One function of the linkage 324 in thethreaded plug embodiment is to resist rotation of the plug duringrotation of the key. Thus, if an alternative to linkage 324 such as amultistrand braided cable is used, some additional registering structureshould be provided to resist rotation of the threaded plug.

In use, the threaded plug is engaged within the key 330, and withdrawnby rotation of the key 330 to retract the platen 316 to the loadedposition. While the platen is being retracted against the spring bias,the first linkage 327 and second linkage 329 become extended to theiraxial limit.

After installation of the medication bag, the key is removed by reverserotation with respect to the housing, and the linkage assembly 324 canbe collapsed back into the housing, as illustrated in FIG. 41, bypressing upon the proximal end 325. Preferably, releasable retentionstructures are provided for retaining the proximal end 325 within oragainst the housing, to maintain the outer profile of the pump at aminimum during the dispensation cycle. For example, any of a variety ofrecesses and snap-fit interrelationships between the proximal end 325and the housing can be incorporated, which take advantage of the plasticdeformability of the materials of the housing.

In accordance with one embodiment of this aspect of the presentinvention, the linkage assembly 324 is configured so that the maximumlength between the proximal end 325 and distal end 326 is about 1.0inches. Thus, a coil spring having a relaxed length of about 7 incheswill be permitted to expand no more than about 1.0 inches in axiallength by the end of the dispensation cycle. Preferably, the loadedinfusion pump 314 will have a thickness of no more than about 1.2-1.6inches, so that the collapsed distance between proximal end 325 anddistal end 326 of linkage assembly 324 is within the range of from about0.3 to about 0.5 inches.

Linkages 327 and 329 can be manufactured in any of a variety of wayswhich will be well known to those of skill in the art. For example,linkages 327 and 329 may be pressed or stamped from sheet metal stock,such as aluminum or stainless steel, and thereafter drilled or punchedwith the appropriate slots and pivot holes, or may be molded from any ofa variety of plastic moldable materials having sufficient strength forthis intended application.

In one embodiment of the invention, linkages 327 and 329 are punched outof 0.1 inch thick stainless steel sheet, with a width of about 0.25inches and a length of about 0.6 inches. The axial length of the slot isabout 0.4 inches, and pivots are formed using rivets, screws or thelike.

In an alternate embodiment, the first and second linkages are pivotallyconnected together without the use of a slip joint. This constructionmay extend pivot 331 (FIG. 41) farther in a lateral direction than pivot332 (FIG. 42) when the platen is in the retracted position and theproximal end 325 of linkage 324 is pressed back inside the housing.Depending upon other design parameters, as will be apparent, theembodiment of FIG. 42 may be utilized with a relatively smaller diameterspring 320.

As a further alternative, the linkage connection comprises a unitarylink 327′, as illustrated in FIG. 43. As will be apparent to one ofskill in the art, the outer profile of an infusion pump having thelinkage 327′ of FIG. 43 will be relatively larger than an embodimenthaving a collapsible linkage assembly. In addition, compressive forcesuch as by the patient upon the threaded plug 325 in the embodimentillustrated in FIG. 43 will be additive to the spring force, andpotentially cause changes in the effluent fluid flow rate. Thus, thisembodiment, although relatively simply to manufacture, may be desirablyutilized only in circumstances where the outer profile and compressionissues are not of concern.

The foregoing designs have been determined to produce a relativelyconstant output profile throughout the dispensation cycle of devicesincorporating these designs. However, even with reasonable prestressingof the spring, output pressure generally declines over the dispensationcycle as the spring relaxes and the pressure contact area on the bagchanges. Provision of a spring having a higher spring constant or higherpretension can change the starting force and ending force throughout adispensation cycle, but generally not appreciably flatten the outputforce or contact area profile.

In a test where the internal pressure of the bag was maintained at aconstant 5 lbs./in² while the contents were delivered, it was found thatthe force applied to the bag needed to be increased from 24 lbs. forceat the beginning of the dispensation cycle to 40 lbs. force near thecompletion of the dispensation cycle. See FIG. 60.

Thus, in accordance with a further aspect of the present invention,there is provided an element for introducing a drag or resistance todistal travel of the platen to produce a flattening of the outputpressure profile. Preferably, the amount of drag on the distal movementof the platen changes continuously over a portion or all of thedispensation cycle, having a maximum value at the commencement of thedispensation cycle and reaching a minimum value at some point betweenthe commencement and end of the dispensation cycle. Preferably, thedeclining drag provided by the drag elements complements the decliningspring force throughout the dispensation cycle in a manner that producesa substantially flat net spring and bag contact area and forcethroughout the dispensation cycle. Of the two, the changing bag contactarea is a greater negative influence than the declining spring force.

Thus, referring to FIG. 44, there is disclosed an infusion pump 334having one or more springs 336 for biasing a platen 338 against amedication bag 340. Platen 338 is provided with at least one dragelement 342 for contacting a friction surface 344 throughout at least aportion of its axial length of travel. Drag element 342 can be providedin any of a variety of forms, and can extend radially outwardly withinthe plane of the platen 338, or be spaced apart axially from the planeof the platen, such as is illustrated in FIG. 44.

In the illustrated embodiment, drag element 342 comprises an axiallyextending support 345, having a generally transverse element 346 at theproximal end thereof. Element 346 engages at least one friction surface344, which, in the illustrated embodiment, ramps radially outwardly awayfrom element 346 as the element 346 travels in the distal direction.Element 342 preferably comprises a resilient material such as a rubberor other elastomer, such as neoprene.

Element 346 and surface 344 can take any of a variety of configurations.For example, in the illustrated embodiment, element 346 can take theshape of a circular disk, extending within a generally frusto-conicallyshaped well, having annular surface 344 extending around the well.Alternatively, surface 344 can be provided on only one side or opposingsides of a bilaterally symmetrical element 342. Retraction of platen 338in the proximal direction forces element 342 against surface 344, toprovide a relatively tight fit, which dissipates as element 342 is drawnaxially in the distal direction.

In a simplified embodiment, the interior wall of the pump housing isramped or stepped slightly in the radially inward direction along all ora portion of its interior circumference. This ramped or stepped regionextends radially inwardly in the proximal direction, so that thesmallest cross-sectional area occurs at the beginning of thedispensation cycle. At that point, the radially exterior edge of theplaten 338 frictionally engages the step or ramp to provide a resistanceto distal travel which dissipates or disappears at some point along thedistal travel of the platen.

In general, in a stepped friction surface embodiment, the step willextend throughout no more than about the first one half or one third ofthe travel. However, the extent of friction desired and the rate oftaper or location of the distal edge of the step will vary dependingupon the spring constant and amount of prestress, and the bag contactarea, and can be optimized for any particular embodiment through routineexperimentation by one of skill in the art.

In accordance with one embodiment of the present invention, a dragelement is constructed as shown in FIG. 44. A 50 cc medication bag isinserted within the infusion pump, and the change in spring forceexerted against the bag, as well as the drag due to the resistanceelement, are measured at each 10-cc increment of fluid dispensation. Thefollowing results are obtained:

TABLE 1 output pressure net change output w/o drag drag w/ drag w/ dragfill spring force element w/ element element element 50 ml 40 lbs.   +8psi  −13 lbs. 0 5 psi 40 ml 39 lbs.   +7 psi  −11 lbs. 0 5 psi 30 ml 38lbs. +5.9 psi −8.8 lbs. 0 5 psi 20 ml 37 lbs. +4.4 psi −6.4 lbs. 0 5 psi10 ml 36 lbs. +2.4 psi −3.4 lbs. 0 5 psi  0 ml 35 lbs.     0 psi     0lbs. 0 5 psi

In accordance with a further aspect of the present invention, there isprovided an indicium of the status of the dispensation cycle, which canbe readily incorporated into any of the previously disclosedembodiments. Referring to FIG. 45, there is disclosed a fluid medicationbag 348, positioned between a platen 349 and the base 350 of an infusionpump. Preferably, at least a portion of base 350 comprises a transparentwindow 352, such as polycarbonate or clear polypropylene, or othermaterials well known in the art. Disposed between the medication bag 348and the platen 349 is a membrane 354, which will be discussed in detailinfra.

The platen 349, or a cover for the platen, is provided with at least oneembossed symbol 356, such as an E indicating “empty.” The embossedsymbol is preferably raised from the planar surface of the platen.

When the medication has been fully expelled from bag 348, the embossedsymbol 356 is pressed by the platen 349 into the membrane 354 and thesymbol 356 embossed on the platen becomes visible through the window 352in the base 350 of the infusion pump. For this purpose, membrane 354 maycomprise any of a variety of materials such as rubber or silicone.Membrane 354 is preferably has a thickness within the range of fromabout 0.020 inches to about 0.030 inches. However, the thickness of themembrane 354 and material can be varied considerably, depending upon thenative pigmentation in the membrane and compressibility under the forcedue to the spring. The embossed letters are preferably raised to aheight of about 0.04 inches from the surface of the platen.

Referring to FIGS. 48 through 51, there is disclosed an ultra lowprofile sliding spring retractor embodiment in accordance with a furtheraspect of the present invention. Infusion pump 360 is provided with ahousing 362, having a platen 366 contained therein which is biased inthe direction of a fluid medication bag 368 by one or more springs 364.In the illustrated embodiment, four coil springs 364 are provided, eachhaving a generally conical configuration so that the axial length of thecompressed spring is no more than the diameter of the spring coil wire,as illustrated in FIG. 50.

The platen 366 is retracted against the bias from spring 364 by one ormore levers 374 movably disposed along an inclined path such as slot 370with respect to the housing 362. Preferably, at least one pair ofopposing levers 374 and 376 are provided, and, in the illustratedembodiment, a second pair of levers 375 and 377 are also provided.Referring to FIG. 49, lever 374 rides in a slot 370 formed in a housing362. Slot 370 is inclined from a first end 371 to a second end 379 in anaxial and medial direction. Similarly, lever 375 travels in slot 372,which inclines medially in the axial direction. In this manner, the usercan place a thumb on lever 375 and a forefinger on lever 374, andcompress the two levers together to advance the platen against thespring bias. Inclusion of a mirror image pair of levers 376 and 377 fortraveling in corresponding inclined slots (not illustrated) on theopposite side of the housing 362, the amount of force required to beexerted by each hand of the user is divided in half, and provides a moreconvenient force distribution within the platen pump 360.

In one embodiment of the invention, each of levers 374, 375, 376 and 377are separately movably mounted within their respective slots in thehousing 362. For example, each lever is integrally molded with orsecured to the platen 366, and, preferably, provided with a bearing suchas a roller bearing (not illustrated) for minimizing friction duringreciprocal travel within the corresponding inclined path of travel.

Alternatively, each opposing member of a pair of levers are joinedthrough the center of the device, to provide a single post extendingtherethrough. For example, lever 374 and 376 can comprise opposite endsof a single shaft, which extends through or adjacent to the platen 366.This design simplifies the construction of the pump in some aspects,such as by eliminating the torque which would otherwise occur at bearingand or connecting of the lever to the platen 366. The unitary post caneither be permanently mounted within the housing, or removablypositionable within a through lumen, so that the posts can be removedfrom the unit once the medication bag has been inserted.

In the illustrated embodiment, opposing levers 374 and 376 are oppositeends of a unitary post, and opposing levers 375 and 377 are similarlyopposing ends of a unitary post. The posts in this embodiment extendalong the medication bag 368 side of platen 366, as is illustrated inFIGS. 50 and 51. FIG. 50 illustrates a side elevational view of anembodiment of the invention in which the posts are retained in theretracted position, such as for insertion of the medication bag 368.FIG. 51 illustrates a point in the dispensation cycle of the embodimentof FIG. 50, with the posts remaining in position adjacent the platen366.

Referring to FIG. 49, the medial most extent 379 of the path of travelfor lever 374 is provided with a detent 380, for removably retaining thelever 374 at the fully retracted position such as during loading. Aftereach of the levers has been advanced to the detent 380, the platen 366will be releasably retained in the retracted position to permitinsertion of a fluid medication bag 368 between the platen 366 and thebottom of housing 362. This can be accomplished in any of a variety ofways disclosed elsewhere herein, such as by introduction of the fluidbag 368 through a side opening in the housing 362, or by providing thehousing 362 with a hinged bottom wall which can be opened to insert thefluid medication bag 368. Following installation of the bag, each lever374 can be advanced laterally slightly out of the corresponding detent380, so that the lever 374 is no longer retaining the spring bias. Thelevers thereafter may be withdrawn from the device, or folded at a hingepoint (not illustrated) to reduce the peripheral profile of the device.

Preferably, the angle of the path of travel of lever 374, which, in theillustrated embodiment is governed by the angle of the slot 370 iswithin the range of from about 10° to about 20° from the plane of thecentral region of the platen 366. As will be apparent to one of skill inthe art, as the axis of the path of travel of lever 374 approachesperpendicular to the plane of the platen (ie. approaches thelongitudinal axis of travel of spring 364), the leverage obtained inadvancing the platen against the spring bias diminishes. Thus, in oneembodiment, the slot 370 could extend at a perpendicular to the plane ofthe platen. However, the patient would be required to exert asignificant force in order to retract the platen against the springbias.

The lower limit on the range of angles between the path of travel oflever 374 and plane of platen 366 is governed by several factors. Theaxial component of the path of travel must be sufficient to fullyretract the platen 366 so that a medication bag 368 can be inserted.Thus, as the angle decreases beyond a certain limit, the length of thepath of travel must be increased to obtain the same axial component,thereby requiring a larger outer peripheral dimension of the device. Inone preferred embodiment, the housing 362 has a length of about 5 inchesand a thickness along the longitudinal axis of spring 364 of about 0.9inches. Slot 370 inclines at an angle of about 15° from the plane of thecentral region of the platen 366, and has a length of about 2.2 inches.

In accordance with a further embodiment of the present invention, thereis provided an improved spring biased intravenous infusion pump having aparallelogram “scissor”-type linkage for transferring spring force tothe medication reservoir. Referring to FIG. 52, the pump 400 comprises ahousing 401 which may be formed as an integral unit, or from two or moredetachably connected components as has been previously described.

Referring to FIGS. 53 and 54, the preferred detachable component housing401 comprises a cover 402 and a base 404. Each of the cover 402 and thebase 404 contain an annular wall 442 and 444 extending in the axialdirection. Complementary threads are preferably provided on the outersurface of the annular wall 442 of the base 404 and inner surface of theannular wall 444 of the cover 402, to facilitate threadable engagementof the cover 402 and base 404 as has been discussed. Alternatively, thecontacting surfaces of the cover 402 and base 404 are provided withcomplementary pins and J- or L-shaped grooves to permit apress-and-twist fit interlock. Any of a variety of alternativeinterlocking structures may be utilized for the housing 401 of theinvention, as will be apparent from the previous disclosures herein.

The cover 402 and base 404 are preferably formed in accordance withconventional techniques for the production of medical device housings,such as injection molding of thermoplastic or thermoset polymers.Alternatively, any of a variety of other techniques may be utilized,including fabrication from sheet metal stock, as will be well understoodby one of skill in the art.

In general, base 404, annular wall 442, annular wall 444 and cover 402cooperate to form a chamber 446 for containing the functional componentsof the infusion device. In the illustrated embodiment, a platen 410 isbiased against a reservoir such as a flexible medication bag 406 bymeans of a spring and linkage assembly 411.

Fluid bag 406 is in fluid communication with the patient by way ofeffluent fluid line 448, which extends through the housing 401 by way ofa port 450. Modification of the port 450 to accommodate the variousrelationships between the cover 402 and base 404 will be apparent to oneof skill in the art. A flow regulator (not illustrated) to regulate theflow of medication is provided on fluid line 448.

In general, the fluid bag diameters contemplated for use in accordancewith the present invention are in the area of from about 3.5 inches indiameter to about 5 inches in diameter and from about 0.5 inches toabout 1.0 inches thick. However, infusion pumps adapted to receive othersize bags can be readily produced in accordance with the disclosureherein.

Referring to FIGS. 53 and 54, the platen 410 embodiment designed for usewith a 3.8 inch diameter, one inch thick, 100 cc. medication bag 406 hasboth a flat, circular central contact surface 413, having a diameterwithin the range of from about 2.4 to about 2.8 inches, and an annularring portion 415 which inclines away from the reservoir contacting sideof platen 410. The outside diameter of annular ring portion 415 isgenerally within the range of from about 3.4 to about 3.6 inches for usewith a 3.8-inch diameter flat medication bag 406. Medication bag 406 isapproximately 3.5 inches in diameter when full. The angle of the surfaceof annular ring portion 415 with respect to an extension of the plane ofcentral contact surface 413 is preferably within the range of from about10° to about 45°, and more preferably within the range of from about 10°to about 30°.

In general, the transition 417 between the central contact surface 413and the radially inwardmost extent of annular ring portion 415 ispositioned so that the circular central contact surface 413substantially completely covers the planar portion on the upper surfaceof fluid medication bag 406. Referring to FIG. 53, medication bag 406comprises a generally planar upper surface, having an outer limit ortransition 407 where the peripheral region of bag 406 commencesdeviation from the plane of upper surface 409.

As illustrated in FIG. 53, the transition point 407 on the bag 406 isroughly coincident with the transition point 417 on the platen 410.Referring to FIG. 54, the interior surface of bottom plate 408 isconfigured with a complementary nesting surface for platen 410.Preferably, platen 410 contains a guide 425 such as an annular flangeextending in the axial direction for stabilizing the platen 410 as itcompresses the medication bag 406 against the base 404 of the housing401.

The platen 410 is biased towards the medication bag 406 through alinkage assembly 411. In general, linkage assembly 411 comprises one ormore biasing elements having a longitudinal axis which extends at anangle with respect to the longitudinal axis of travel of platen 410.Preferably, the biasing element axis extends approximately at about aperpendicular to the axis of travel of platen 410. As is discussedbelow, the biasing element preferably comprises one or more springshaving at least one concentric or parallel spring guide such as acentral shaft or tubular cover.

In the illustrated embodiment, a spring guide 414 extends along an axiswhich is generally perpendicular to the axial direction of travel ofplaten 410. The spring guide 414 conveniently comprises a threaded metalrod having a length within the range of from about 3.0 to about 3.4inches, and a diameter from about 0.125 inches to about 0.250 inches,although variations will be readily apparent to one of skill in the art.

In an embodiment in which the spring guide 414 comprises a unitary orsegmented shaft having a continuous thread extending throughout itslength, a tubular sleeve may be conveniently disposed over the portionsof the threaded shaft which will slidably carry other moving parts, aswill be discussed. Alternatively, the spring guide 414 can beconstructed from a generally smooth rod, having a threaded region onlyon the distal ends thereof for receiving nuts 416 and 416′.

A spring stop is carried at either end of the spring guide 414. As willbe readily apparent to one of skill in the art, any of a variety ofmeans can be utilized for retaining a spring under tension. For example,a nut or nut and washer threadably engaged to the spring guide 414 isconvenient, both from a manufacturing standpoint, and due to the abilityof the manufacturer to adjust the spring tension by simply rotating thenut.

In the illustrated embodiment, a spring stop 419 is provided on eachlateral end of the spring guide 414 for limiting the lateral expansionof each spring. The spring stop 419 generally comprises a radiallyoutwardly extending annular flange 423, having an aperture 421 extendingaxially therethrough for receiving a threaded portion of spring guide414. Spring stop 419 also has a cross-sectional area through a radialplane sufficient to limit expansion of the spring. Each spring stop 419is preferably provided with an axially extending tubular sleeve 418 and418′, which in the assembled pump extends medially along the springguide 414 and within the spring. In the illustrated embodiment, thesleeves 418 and 418′ have internal threads complementary to the threadon spring guide 414 to securely threadably retain the spring stop 419 inplace.

In an alternate embodiment (not illustrated), the spring stop 419comprises a radially outwardly extending annular flange 423 and anaxially extending tubular sleeve 418, as in the foregoing embodiment.However, the spring stop 419 is held in place by a threaded nut secureddirectly to the spring guide 414 on the lateral side of outwardlyextending annular flange 423. In this embodiment, the internal thread onaperture 421 and interior wall of axially extending tubular sleeve 418is unnecessary. Although the use of a lateral threaded nut is convenientfrom a manufacturing standpoint, it adds to the overall lateral lengthof the spring guide 414, which may be undesirable in a given embodiment.

The springs 412 and 412′ are compressed between the spring stops 419 andtwo axially moveable blocks 420 and 420′. In one embodiment, the springs412 and 412′ comprise music wire having a wire diameter of approximately0.085 inches. Lower diameters such as 0.080 may also be used byincreasing the preload.

Preferably, springs 412 and 412′ have a spring constant within the rangeof from about 80 lbs. per inch to 130 lbs. per inch in a dual springembodiment. Each spring 412 and 412′ is approximately 1.7 inches long inits un-compressed state and approximately 0.9 inches long in its fullycompressed state, shown in FIG. 53, and ½ inch in diameter. The sum ofthe axial travel of springs 412 and 412′ is approximately 0.7 inchbetween the compressed state as shown in FIG. 53 at the beginning of thedispensation cycle and the state shown in FIG. 54 at the end of thedispensation cycle.

Blocks 420 and 420′ function as medial spring abutments to mechanicallylink the medial travel of the spring to the linkage assembly 411 andplaten 410. In the illustrated embodiment, blocks 420 and 420′ aregenerally rectangular in exterior configuration and contain an annularor tubular recess 422 on the lateral side which does not go through theentire axial length of the block 420 and 420′. The springs 412 and 412′fit into the recess 422 in each block 420 and 420′. The blocks 420 and420′ also contain an axially extending tubular opening through thecenter of the block to allow the blocks to slide axially along thespring guide 414.

Each block 420 and 420′ may comprise any of a variety of durablematerials such as aluminum, stainless steel or other metal known in themedical device arts. Preferably, however, a strong lightweight plasticmaterial such as DELRIN available from DuPont is used. Polymeric blocksor coatings are preferred, due to their ability to slide relativelyfreely on the spring guide 414 when biased by the springs 412 and 412′.

Each of two opposing sides of the blocks 420 and 420′ parallel to thespring guide 414 contains a block pivot 438. The relative positioning ofpivots and corresponding recesses discussed herein can readily bereversed, as will be apparent to one of skill in the art.

Two link arms 424 and 426 are pivotably affixed to one pivot 438 at afirst end thereof. Link arm 424 is connected at a second end to ananchor pivot 436 which is connected to the cover 402. Link arm 426 isconnected at its second end to a platen pivot 434 which is connected tothe platen 410. Link arms 424 and 426 form a scissor-type configurationwhich is a mirror image of the configuration of link arms 428 and 430.Together, the four link arms 424, 426, 428 and 430 form an adjustableparallelogram linkage, as will be understood by one of skill in the art.Preferably, an identical parallelogram linkage exists on the opposingvertical wall of blocks 420 and 420′, as shown in FIG. 55.

Anchor pivot 436 is secured to attachment 432, which is preferably fixedto cover 402. Platen pivot 434 is affixed to platen attachment 440,which is preferably pivotably attached to platen 410.

In a preferred embodiment, platen attachment 440 is provided with anupper cam shaped profile that is shaped and sized to follow the path ofthe lower inside edge of each of blocks 420 and 420′. Suitable camshaped surfaces can be provided by either an annular, dome shapedelement 440, or by providing one or more generally parallel planerelements having a cam shaped outer profile, as will be apparent to oneof skill in the art. Provision of a cam surface which tracks the path ofthe lower inside edge of the blocks 420 and 420′ operates to limit theextent to which the plane of platen 410 is permitted to deviate from itsnormal position which is generally parallel to the plane of the bottomplate 408. Preferably, the outer surface of the cam shaped portion ofanchor 440 is sufficiently close to the path of travel of each of blocks420 and 420′ so that the tilt of the platen is limited no more thanabout 5%.

As a further option on the scissor embodiment of the present invention,a fluid level indictor 451 is provided. See FIG. 54. Fluid levelindicator 451 generally comprises a linkage 452 which is pivotablyconnected to a moving portion of the scissor assembly, and also to thefluid level indicator 451. Level indicator 451 is preferably slidablymounted in a track 454 adjacent a scale (not illustrated) and calibratedsuch that the level indicator 451 and scale will indicate the remainingfluid volume.

After a medication bag 406 has been inserted into the base 404 and thebase 404 engaged with the cover 402, the springs 412 and 412′ are attheir point of highest compression. As the springs 412 and 412′ releaseforce in a direction perpendicular to the axial direction of platentravel, the blocks 420 and 420′ slide towards each other on spring guide414, causing the medial ends of link arms 424, 426, 428 and 430 to movefurther apart in the axial direction. Through this mechanism the forceexerted by the springs 412 and 412′ is transmitted through the link arms424, 426, 428 and 430 to the platen 410 through the platen attachment440. The spring force component transmitted by the link arms 424, 426,428 and 430 to the platen 410 increases throughout the dispensationcycle as the tension of the spring decreases so as to maintain asurprisingly substantially constant medication output pressure until thebag is substantially collapsed, as shown in FIG. 54. This surprisingresult shown in the experiments discussed infra is desirable inapplications such as infusion of chemotherapy chemicals into a patientover a period of time at a constant rate. The mechanical advantageobtained by the link arms 424, 426, 428 and 430 compensates for thedecrease in spring tension and the increase in the bag contact area overthe dispensation cycle.

EXPERIMENT 1 Constructing the Pump

A platen was constructed in accordance with the embodiment illustratedin FIGS. 52-55, having springs 412 and 412′ comprised of music wirehaving a wire diameter of approximately 0.085 inch. Springs 412 and 412′had an outside diameter of about 0.5 inches, a spring constant ofapproximately 111 lbs. per inch, and were approximately 1.7 inches longin the uncompressed state and approximately 0.9 inch long in the fullycompressed state, as shown in FIG. 54. The sum of the axial travel ofsprings 412 and 412′ was approximately 0.7 inch between the compressedstate as shown in FIG. 53 at the beginning of the dispensation cycle andthe state shown in FIG. 54 at the end of the dispensation cycle. Thesprings were preloaded to about 35 lbs. on each side, and were measuredto generate a total spring force of about 160 lbs. Blocks 420 and 420′were constructed from DERLIN, available from DuPont. The length of eachof the four link arms was about 0.8 inches from pivot to pivot. Theplaten and opposing wall were substantially flat to isolate the pressureeffects due to the spring biasing assembly.

EXPERIMENT 2 Testing the Platen Pump

A 50 cc medication bag 406 was inserted in the platen pump of Experiment1 and the output fluid pressure from the medication bag 406 was measuredas the volume in the medication bag 406 decreased over the dispensationcycle. Table I below illustrates the data accumulated from thisexperiment.

TABLE I Volume Expelled from Output Fluid Medication Bag (cc) Pressure(psi) 0 5.0 .5 5.0 1 5.0 2 5.0 3 5.0 4 5.0 5 5.0 10 5.0 15 5.05 20 5.125 5.1 30 5.1 35 5.1 40 4.95 42.5 4.6 45 4.45 46 4.25 47 4.1 47.5 9.0 483.9 48.5 3.5 49 2.4 50 0

The data obtained from the above experiment is reproduced in FIG. 56,which plots the volume of medication dispelled in cubic centimetersversus the output pressure in lbs/sq. in. The percent change in outputpressure versus the volume expelled is illustrated in FIG. 57. FIG. 57illustrates the remarkably steady output pressure of the medicationcontained in medication bag 406 during the dispensation cycle producedby the platen pump 400.

EXPERIMENT 3 100 cc Volume Test

In Experiment 3, the 50 cc medication bag 406 was replaced with a 100 ccmedication bag. The experiment conducted in Experiment 2 above wasrepeated and the following data was recorded.

TABLE II Volume Expelled from Output Fluid Medication Bag (cc) Pressure(psi)  0 5.1  5 4.6 10 4.7 20 4.75 30 4.75 40 4.6 50 4.55 60 4.4 70 4.280 3.95 90 3.6 95 3.4 99 2.9 100  0

FIG. 58 illustrates the output pressure over the dispensation cycle.FIG. 59 illustrates the percent change in pressure over the dispensationcycle.

Increasing the volume of medication in the medication bag 406 from 50 ccto 100 cc remarkably did not dramatically affect the change in pressureover the dispensation cycle on the medication bag 406.

Referring to FIGS. 61-65, a fluid container 500 is provided which may bereadily used with any of the previously disclosed embodiments of theplaten pump. Preferably, the fluid container 500 consists of acollapsible medication reservoir or bag 510 in fluid communication withan effluent fluid line 530. The effluent fluid line 530 may lead to anadministration set 540 shown in phantom in FIG. 61. An administrationset is also shown in FIG. 7. The effluent fluid line 530 may be standardPVC tubing or other material known to those skilled in the art.

Preferably, the medication reservoir 510 has a first surface 508 and asecond generally opposing surface 509. The first surface 508 and secondsurface 509 each have a substantially planar central portion 512 and513. In a medication reservoir having a diameter of about 3.5 inches,the generally planar central portions 512 and 513 typically have adiameter in the range of from about 1.5 inches to about 3.0 inches, andpreferably from about 2.4 inches to about 2.8 inches in the fully filledconfiguration.

A transition portion 514 surrounds the circular central portions 512 and513 of the first surface 508 and second surface 509. Transition portion514 comprises the portion of the surface of the reservoir 510 whichdeviates from the plane of first surface 508 or second surface 509.Thus, transition 514 joins the flat circular central portions 512 and513 with radially exterior-most sloping portions 516 when the medicationreservoir 510 is full as shown in FIG. 62.

The radially exterior-most opposing sloping portions 516 are preferablyjoined at seam 520. By “seam” the present invention also contemplatesthe outer peripheral edge of a “seamless” bag such as may be producedthrough any of a variety of molding or other plastic forming techniquesknown in the art.

The first surface 508 and second surface 509 are preferably formed fromtwo sheets of a suitably bondable, inelastic material which exhibitssuitable stability in the presence of the intended medication. The twosheets may be joined at seam 520 with the use of any of a variety ofjoining techniques, such as thermal bonding, solvent bonding, adhesivesor by a radio frequency weld. Preferably, the medication reservoir isconstructed from a PVC in U.S. Class 6 adequate for the delivery ofdrugs to a patient although other materials known to those of skill inthe art are available and may be used.

As shown in FIGS. 63 and 65, the effluent fluid line 530 may be joinedto the medication reservoir 510 through the use of a radio frequencyweld or other bond at a joint 525. Other means for joining themedication reservoir 510 and the effluent fluid line 530, such asthermal bonding, solvent bonding, adhesives or friction couplings willbe readily apparent to those of skill in the art.

Preferably, the medication reservoir 510 shown in FIGS. 61-65 has adiameter within the range of from about 3.5 inches to about 5 inches anda height within the range of from about 0.5 inches to 1.0 inches. Ingeneral, the diameter of the bag is influenced by the type ofcompression mechanism used. For example, in the threaded clam shellembodiment of FIG. 1, a bag having a diameter of much greater than aboutfour inches would require a pump having too big a diameter to beconveniently grasped by many patients. Other compression mechanisms,however, can be readily used with 5 inch, 6 inch, or larger diameterbags. The height, or thickness of the bag is typically governed by thedesired volume and the maximum desired diameter.

For many applications of the present invention, the fluid container 500preferably contains 50 cc of fluid. Although these volumes are preferredin the present invention, other sizes of fluid containers may be easilyconstructed using the disclosure of the present invention. These varyingsize fluid containers are contemplated by this disclosure.

An important aspect of the fluid container 500 is that it is able towithstand pressures applied to it by the platen pump disclosed herein.Further, preferably the fluid container 500 is relatively inelastic inorder to minimize the change in pressure on the fluid by the platenpump, Advantageously, the disc like configuration of the presentembodiment of the fluid container 500 results in substantially evenpressure distribution throughout seam 520 when the medication reservoir510 and effluent fluid line 530 are in the dispensation cycle. Asdiscussed above, this uniform pressure distribution minimizes thebuildup of localized stresses which could lead to a rupture of thecontainer 500.

Another advantage of the fluid container 500 is that a plurality offilled fluid containers 500 may be easily stored such as in arefrigerator in a stacked configuration. Further, when the fluidcontainers 500 are empty, the volume required to dispose of them is verysmall because the fluid containers 500 are flat and flexible when empty.

In addition to a fluid container with a circular outer profile, othershaped reservoirs may be constructed in accordance with the disclosureof the present invention. For example, referring to FIGS. 66-69, asquare medication reservoir 560 having a generally planar square topsurface 562 and bottom surface 563 may be used in connection with thevarious embodiments of the platen pump. In a similar fashion to thecircular medication reservoir, the top and bottom surfaces of the squaremedication reservoir 560 have generally square flat central portions,transition portions 564 and radially exterior-most sloping portions 566.Preferably, a high frequency weld is used to join seam 572 and attachthe medication bag 560 to the effluent fluid line 570 at a joint 568.

Referring to FIGS. 70-73, a diamond-shaped fluid reservoir 561 may beprovided. Further, a hexagonal fluid reservoir 580 and 581 (FIGS. 74-81)with a joint 582 on one of the sides of the hexagonal medicationreservoir 580 (FIGS. 74-77) or a joint 583 at one of the comers of thehexagonal medication reservoir 581 (FIGS. 78-81) may be provided.Referring to FIGS. 82-89, fluid containers having medication reservoirswith eight sides (586), ten sides (588), twelve sides (590) ortwenty-four sides (592) may be provided.

In a further embodiment, the present invention includes a platen pumpdesigned for use with rectangular medication bags. Referring to FIG. 90,the pump 600 comprises a housing 601 formed from a cover 602 and a base604. The cover 602 and base 604 are preferably formed in accordance withconventional techniques for the production of medical device housings,such as injection molding of thermoplastic or thermoset polymers.Alternatively, any of a variety of other techniques may be utilized,including fabrication from sheet metal stock, as will be well understoodby one of skill in the art.

A handle storage recess 608 may be formed in the cover 602 duringfabrication. As will be described below, a handle 610 is used to raiseand lower the platen in the pump 600. When the platen is applying forceto a medication bag (not shown), the handle 610 preferably separatesfrom the pump 600. The handle 610 can be inserted into the handlestorage recess 608, providing a convenient location to store the handle610 when not in use. A lift tab 609 may be included on the handle 610.The lift tab 609 provides assistance to the user in removing the handle610 from the handle storage recess 608.

The cover 602 also may contain a ridge 612. In one embodiment, the ridge612 is formed as a mound with an aperture 614 in the center of the ridge612 for insertion of the handle 610. However, other configurations forthe ridge 612 are contemplated as will be easily understood by those ofskill in the art. A portion of the handle 610 is preferably spaced abovethe cover 602 in operation, thereby allowing a user to turn the handle610 without interference from the cover 602.

A connecting tab 613 may be located on a face 619 of the base 604. Theconnecting tab 613 includes an aperture 615. Because the pump 600 isdesigned to be carried over an extended period of time by the patient,the connecting tab 613 provides a convenient way to tote the pump 600. Asplit ring, string or other material can be placed through the aperture615 in the connecting tab 613. The pump 600 can then be secured to anI.V. pole or a patient. Of course, the connecting tab 613 may beintegral with the cover 602. In addition, other connecting means may beused to assist a patient in transporting the pump 600.

FIG. 91 shows an exploded view of the pump 600. The pump 600 includesthe cover 602, the handle 610, a spring and linkage assembly 620, aplaten 630, a connecting bolt 645 and the base 604. A rectangularmedication bag 640 is inserted into the base 604 during pump 600operation to provide a medication reservoir.

The cover 602 has an outer rim 606. This outer rim 606 slidably engagesa corresponding groove 616 in the base 604. When the rim 606 of thecover 602 is inserted into the groove 616 of the base 604, the base 604and cover 602 cooperate to form a chamber 646 for containing thefunctional components of the infusion device and the medication bag 640.Alternatively, the base 604 may contain a rim and the cover 602 maycontain a groove for slidable engagement of the cover 602 and the base604.

In the illustrated embodiment, the spring and linkage assembly 620 isconnected between the platen 630 and the cover 602. The spring andlinkage assembly 620 contains connector bars 624-627 (FIG. 92). A pairof bar receivers 632 and 634 are formed on the top side 631 of theplaten 630. The connector bars 624 and 627 insert in the bar receivers632 and 634. A corresponding pair of bar receivers (not shown) arelocated on a bottom side of the cover 602. The connector bars 625 and626 insert in the bar receivers of the cover 602. This connectionsecures the spring and linkage assembly 620 between the platen 630 andthe cover 602.

As shown in FIG. 91, the connecting bolt 645 is preferably insertedthrough an aperture 636 in the platen 630, through an aperture 622formed by movable blocks 621 and 623 and through the aperture 614 in thecover 602. A threaded bore 611 of handle 610 has threads correspondingto threads 646 on the connecting bolt 645. The threads in the handle 610engage with the threads 646 on the bolt 645 allowing movement of theplaten 630 via the spring and linkage assembly 620 upon turning thehandle 610, as will be described below. When the handle 610 is fullyengaged with the bolt 645, the pump 600 is in an open position. When thepump 600 is in the open position, the platen 630 is fully stored withinthe cover 602. This allows the cover 602 to separate from the base 604without interference from the platen 630. As the handle 610 is turned toseparate the handle 610 from the bolt 645, the platen 630 begins tolower into the base 604 via the spring and linkage assembly 620.

The medication bag 640 is preferably in fluid communication with thepatient by way of an effluent fluid line 648, which extends through thebase 604 by way of a port 650. Modification of the port 650 toaccommodate the various relationships between the cover 602 and base 604will be apparent to one of skill in the art. A flow regulator (notillustrated) to regulate the flow of medication may be provided on fluidline 648.

In general, the medication bags 640 contemplated for use in accordancewith this embodiment of the present invention are standard medicationbags well known and used in the art. Standard bags are currentlyproduced by Abbott Laboratories and Baxter Healthcare. However,medication bags adapted for use in the pump 600 can be readily producedin accordance with the disclosure herein. The medication bags 640include a fluid reservoir segment 641, an injection port 642 and a fluiddelivery port 644.

When delivering medication from a medication bag 640 to a patient, onlythe fluid reservoir segment 641 is compressed by the platen 630. Theinjection port 642 and the fluid delivery port 644 are generally notcompressed. The platen 630 is approximately the same size as the fluidreservoir segment 641 of the medication bag 640. To protect both theinjection port 642 and the fluid delivery port 644 of the medication bag640, the base 604 preferably contains walls 652, 654 and 656 forming twocompartments 653 and 655. The injection port 642 fits inside compartment653 and the fluid delivery port 644 fits inside compartment 655. Whenthe medication bag 640 is inside the pump 600, the injection port 642and the fluid delivery port 644 are protected by compartments 653 and655. Only the fluid line 648 is exposed from the pump 600.

Referring to FIGS. 92, 93 and 94, the platen 630 exerts a force on themedication bag 640 through the spring and linkage assembly 620. Ingeneral, the spring and linkage assembly 620 comprises one or morebiasing elements having a longitudinal axis which extends at an anglewith respect to the longitudinal axis of travel of the platen 630.Preferably, the biasing element axis extends approximately at about aperpendicular to the axis of travel of the platen 630. As discussedbelow, the biasing element preferably comprises one or more pairs ofsprings having at least one spring guide such as a central shaft ortubular cover. Because the pump 600 in the preferred embodiment isdesigned to be portable, it is desirable to manufacture the pump as thinand small as possible. To reduce the overall height of the pump 600, twopairs of springs are preferably used as the biasing element. The use oftwo pairs of springs has several advantages. First, the same force isapplied using springs and guides of half the diameter of a single pairof springs. Using springs of a smaller diameter allows the overallheight of the pump 600 to decrease. Second, the lateral spacing of-thesprings assists in providing a balanced force to the platen 630. Byapplying a balanced force, the platen 630 will lower into the base 604with a minimum of rocking.

In the illustrated embodiment, a pair of spring guides 664 and 665extend along an axis which is generally perpendicular to the directionof travel of the platen 630. The spring guides 664 and 665 comprise ametal rod having a length within the range of from about 3 inches toabout 5 inches, and a diameter from about 0.125 inch to about 0.250inch, although variations will be readily apparent to one of skill inthe art.

In an embodiment in which the spring guides 664 and 665 comprise aunitary or segmented shaft having a continuous thread extendingthroughout its length, a tubular sleeve may be conveniently disposedover the portions of the threaded shaft which will slidably carry othermoving parts, as will be discussed. Alternatively, the spring guides 664and 665 can be constructed from a generally smooth rod, having athreaded region only on the distal ends thereof for receiving a nut 670.

A spring stop 675 is carried at either end of the spring guides 664 and665. As will be readily apparent to one of skill in the art, any of avariety of means can be utilized for retaining a spring under tension.For example, a nut or nut and washer threadably engaged to the springguides 664 and 665 is convenient, both from a manufacturing standpointand due to the ability of the manufacturer to adjust the spring tensionby simply rotating the nut. To avoid rotation of the stop 675 on thespring guides 664 and 665, epoxy may be used as will be readilyunderstood by those skilled in the art.

In the illustrated embodiment, a spring stop 675 is provided on eachlateral end of the spring guides 664 and 665 for limiting the expansionof each spring 680. The spring stops 675 generally comprise a radiallyoutwardly extending annular flange 677 and have an aperture 679extending therethrough for receiving a threaded portion of the springguides 664 and 665. The spring stop 675 also has a cross-sectional areasufficient to limit expansion of the spring. The spring stop 675 ispreferably provided with an axially extending tubular sleeve 682, whichin the assembled pump extends along the spring guides 664 and 665 andwithin the spring 680. In the illustrated embodiment, the sleeves 682have internal threads complementary to the threads on the spring guides664 and 665 to securely threadably retain the spring stop 675 in place.

In an alternate embodiment (not illustrated), the spring stop 675comprises the annular flange 677 and the tubular sleeve 682 as in theforegoing embodiment. However, the spring stop 675 is held in place by aseparate threaded nut secured directly to the spring guides 664 and 665.In this embodiment, the internal thread on the aperture 679 and theinterior wall of the tubular sleeve 682 is unnecessary. Although the useof a separate threaded nut is convenient from a manufacturingstandpoint, it adds to the overall lateral length of the spring guides664 and 665, which may be undesirable in a given embodiment.

The springs 680 are compressed between the spring stops 675 and twomoveable stops 621 and 623. In one embodiment, the springs 680 comprisemusic wire having a wire diameter of approximately 0.80 inch. Lowerdiameters such as 0.062 inch may also be used by increasing the preload.

Preferably, the springs 680 have a spring constant within the range offrom about 80 lbs. per inch to 90 lbs. per inch in a dual springembodiment. Each spring 680 is approximately 1.62 inches long in itsun-compressed state and approximately 0.90 inches long in its fullycompressed state, shown in FIG. 93, and 0.50 inch in diameter. The sumof the axial travel of springs 680 is approximately 0.90 inch betweenthe compressed state as shown in FIG. 93 at the beginning of thedispensation cycle and the state shown in FIG. 94 at the end of thedispensation cycle. Depending on the spring constant chosen, thedispensation cycle can vary from one half hour to eight days. Thesedimensions correspond to a pump for a 100 cc medication bag. For largeror smaller medication bags dimensions would vary as will be easilyrecognized by those of skill in the art.

Moveable stops 621 and 623 function as medial spring abutments tomechanically link the medial travel of the spring 680 to the linkageassembly 620 and platen 630. Referring to FIG. 92, the stops 621 and 623are generally rectangular in exterior configuration with a semi-circularcut-out 661 on the interior side. The cut-out 661 may have otherconfigurations as long as the screw 645 fits through the stops 621 and623 when the stops 621 and 623 are in contact with one another. Thestops 621 and 623 also contain annular or tubular recesses 662 which donot extend through the entire length of the stops 621 and 623. Thesprings 680 fit into the recesses 662 in each stop 621 and 623. Thestops 621 and 623 also contain openings 660 through the center of thestops to allow the stops 621 and 623 to slide axially along the springguides 664 and 665.

Each moveable stop 621 and 623 may comprise any of a variety of durablematerials such as aluminum, stainless steel or other metal known in themedical device arts. Preferably, however, a strong lightweight plasticmaterial such as the polymer DELRIN, available from DuPont is used.Polymeric blocks or coatings are preferred, due to their ability toslide relatively freely on the spring guides 664 and 665 when biased bythe springs 680.

Each of two opposing sides of the stops 621 and 623 contain an aperture686. The aperture 686 has internal threads complementary to the threadsof a pivot screw 688. The pivot screws 688 are threadably engaged to thestops 621 and 623 via the aperture 686.

Two link arms 690 and 692 are pivotably affixed to each pivot screw 688at a first end thereof. The link arm 690 is connected at a second end tothe connector bar 625 which is connected to the cover 602. The link arm692 is connected at its second end to the connector bar 624 which isconnected to the platen 630. The link arms 690 and 692 form ascissor-type configuration which is a mirror image of the configurationof link arms 694 and 696. Together, the four link arms 690, 692, 694 and696 form an adjustable parallelogram linkage, as will be understood byone of skill in the art. Preferably, an identical parallelogram linkageexists on the opposing vertical wall of moveable stops 621 and 623, asshown in FIG. 92.

Referring to FIG. 93, after the medication bag 640 has been insertedinto the base 604 and the base 604 is engaged with the cover 602, thesprings 680 are at their point of highest compression. As the springs680 release force in a direction perpendicular to the direction oftravel of the platen 630, the stops 621 and 623 slide toward each otheron the spring guides 664 and 665, causing the second ends of link arms690, 692, 694 and 696 to move further apart. Through this mechanism, theforce exerted by the springs 680 is transmitted through the link arms690, 692, 694 and 696 to the platen 630 through the bar receivers 632and 634. The spring force component transmitted by the link arms 690,692, 694 and 696 to the platen 630 increases throughout the dispensationcycle of the medication bag 640 as the tension of the springs 680decreases so as to maintain a substantially constant medication outputpressure until the medication bag 640 is substantially collapsed, asshown in FIG. 94. Increasing the force throughout the dispensationcycle, as shown above in Experiments 2 and 3, generates a substantiallyconstant output fluid pressure. A constant fluid pressure is highlydesirable for dispensing a variety of drugs such as chemotherapeuticagents. As discussed above, the present invention preferably hasdispensation cycles as long as eight days. During an eight daydispensation cycle, one drop of medication is dispensed approximatelyevery 12 minutes. The ability to maintain a substantially constantoutput fluid pressure is critical in sustaining such a steady flow ofmedication over an extended time frame. Importantly, the force deliveredby the platen 630 on the fluid delivery bag 640 increases through thedispensation cycle resulting in a constant flow rate of medication to apatient.

During the dispensation cycle, it may be desirable to know the amount ofmedication remaining in the medication bag 640. As shown in FIGS. 95 and96, a level indicator is provided on the handle 610. During medicinedispensation, the handle 610 can be inserted in the aperture 614. As themedicine is dispensed from the bag 640, the platen 630 and the bolt 645will move into the chamber 646 of the base 604. As a result, an end 699of the bolt 645 is lowered in the aperture 614. The level indicator 697is calibrated to show the amount of medicine left to be dispensed. Thisamount is determined by the location of the end 699 of the bolt 645.

FIG. 96 shows an alternative embodiment of indicating the medicationlevel. In this embodiment, an indicator 698 is placed on the face 619 ofthe base 604. The indicator 698 can be embodied in many forms, includingaffixing a sticker to the base 604 or incorporated in the injectionmolding. As the medication is dispensed from the medication bag 640, theplaten 630 moves toward the base 604. The remaining fluid level isdetermined by viewing the location of the bottom 635 of the platen 630against the indicator 698.

In operation, a full medication bag 640 is attached to the patient bymeans of a catheter or intravenously via the fluid line 648. The cover602 and the base 604 are separated by turning the handle 610, thusdrawing the platen 630 into the base 602 and slidably disengaging thecover 602 and base 604. The patient inserts the medication bag 640 intothe base 604, ensuring the injection port is inside compartment 653 andthe fluid delivery port is inside compartment 655. The fluid line 648protrudes from the base 604 via the port 650. With the platen 630 fullystored in the cover 602, the cover 602 and the base 604 are slidablyengaged. The patient then turns the handle 610 until it disengages fromthe bolt 645. At this point, the end 699 of the bolt 645 us locatedwithin the aperture 614. The handle 610 may be stored in the handlestorage recess 608. With the handle 610 removed, the linkage assembly620 and platen 630 apply a steadily increasing force on the medicationbag 640 through the dispensation cycle as described above. This forcecauses the platen 630 to compress the medication bag 640, therebyproviding substantially constant fluid flow via the fluid line 648.

After all the medication is dispensed, the patient may remove the handle610 from the handle storage recess 608 and insert the handle 610 intothe aperture 614. The handle 610 is then turned to threadably engage thebolt 645, thereby compressing the linkage assembly 620 and raising theplaten 630 into the cover 602. When the platen is again fully stored inthe cover 602, the cover 602 and the base 604 can be slidablydisengaged. The empty medication bag 640 is removed from the base 604and the pump 600 is ready to repeat the process.

Numerous variations and modifications of the invention will becomereadily apparent to those skilled in the art. Accordingly, the inventionmay be embodied in other specific forms without departing from itsspirit or essential characteristics. The detailed embodiment is to beconsidered in all respects only as illustrative and not restrictive andthe scope of the invention is, therefore, indicated by the appendedclaims rather than by the foregoing description. All changes which comewithin the meaning and range of equivalency of the claims are to beembraced within their scope.

We claim:
 1. An infusion pump for expelling fluid from a flexiblereservoir comprising: a top shell removably connected to a bottom shell,said bottom shell having a non-planar interior bottom surface; apressure plate movably connected to said top shell, said plate having anon-planar surface complementary to said interior bottom surface of saidbottom shell, said pressure plate and said interior bottom surface ofsaid bottom shell defining therebetween a variable-sized area foraccepting the fluid reservoir therein; a shaft positioned between saidtop and bottom shells, said shaft having a first end and a second end; afirst slide and a second slide slidably positioned on said shaft; fourarms defining a parallelogram structure extending between said topshell, said first slide, said second slide, and said pressure plate,said arms rotatably connected to said top shell, said slide members andsaid pressure plate, said slide members and shaft supported by said armsbetween said shells; and biasing means positioned between said first endof said shaft and said first slide and between said second end of saidshaft and said second slide for biasing said slides toward one anotheralong said shaft, thereby biasing said pressure plate through said arms,downwardly towards said bottom shell when said top and bottom shells areconnected.
 2. The infusion pump in accordance with claim 1, wherein saidshells are generally circular in outer shape and threadably engage oneanother.
 3. The infusion pump in accordance with claim 1, wherein saidshells are generally rectangular in shape.
 4. The infusion pump inaccordance with claim 1, wherein said four arms form a firstparallelogram structure and further including a second set of four armsforming a second parallelogram structure, said first and secondstructures positioned on opposite sides of said shaft.
 5. The infusionpump in accordance with claim 1, wherein a stop is positioned at eachend of said shaft, and said biasing means comprises a spring positionedbetween each stop and slide.
 6. An infusion pump for expelling fluidfrom a fluid reservoir comprising: a housing comprising a bottom memberhaving a non-planar inner surface and a top member removably connectedto said bottom member; a platen member movably connected to said topmember, said platen having a non-planar engaging surface which iscomplementary in shape to said inner surface; a first arm having a firstend and a second end, said first end rotatably connected to said topmember and said second end rotatably connected to a first mountingblock; a second arm having a first end and a second end, said first endrotatably connected to said top member and said second end rotatablyconnected to a second mounting block; a shaft having a first end and asecond end, said shaft extending through said blocks; a first springextending between said first end of said shaft and said first block anda second spring extending between said second end of said shaft and saidsecond block; a third arm having a first end and a second end, saidfirst end rotatably connected to said first block and said second endrotatably connected to said platen member; and a fourth arm having afirst end and a second end, said first end rotatably connected to saidsecond block and said second end rotatably connected to said platenmember, whereby said arms form a linkage between said top member, saidblocks, and said platen member, biasing said platen member downwardlytowards said bottom member when said top and bottom members areconnected.
 7. The infusion pump in accordance with claim 6, wherein saidtop and bottom members threadably engage one another.
 8. The infusionpump in accordance with claim 6, wherein said top and bottom membershave a generally circular outer periphery.
 9. The infusion pump inaccordance with claim 6, further including a fluid level indicatorconnected to said housing.
 10. The infusion pump in accordance withclaim 9, wherein said fluid level indicator includes a fluid leveldisplay connected to said top member and an actuator connecting one ofsaid arms with said display.